"A Case of Ed" is the 18th episode of Season 4 and the 95th episode of Ed, Edd n Eddy. In this episode, Edd buys an Encyclopedia of Obscure Diseases, and becomes convinced that he is suffering from a fatal illness when he notices that the symptoms for it describe him perfectly. Not one to waste a pranking opportunity, Eddy uses Edd's sudden hypochondria to entertain himself–that is, when he and Ed aren't busy taunting Kevin, who has been grounded and cannot retaliate.
Kevin stands in a window, staring out grumpily as rolls of toilet paper go flying by and land on his house. The source of these rolls are Ed and Eddy, and the reason that they're even able to do this is explained by Eddy to a disturbed Jimmy: Kevin has been grounded, and so he won't be able to get back at them–at least, not for a while. Soon, however, the duo's merrymaking is interrupted, as Edd arrives, towing behind him a wagon full of used books that he procured from a library sale.
Wanting to share the joy of knowledge with his friends, he picks up one of the books and begins reading from it at random. This book is an Encyclopedia of Obscure Diseases, and the page he is reading details the symptoms of an affliction known as Lackadaisycathro Disease; symptoms which include the rationalization of mundane circumstances, habitual cleanliness, and an abnormal fixation to headwear. Of course, as soon as Edd finishes this description, he is quite worried, as these symptoms are a dead ringer for his personality.
The other two Eds recognize this as well, but Eddy and Ed choose to dismiss it and instead bother Kevin some more. However, when Edd continues to fret after reading more of the symptoms of the disease, Eddy soon makes a joke about how he looks a little sick. Taking this to heart, Edd collapses, giving Eddy the idea to prank Edd by taking advantage of his worried state.
Soon enough, Edd is dressed in a hospital gown, waiting to be seen by Dr. Ed. When Edd is naturally uncertain that Ed is qualified to perform medical procedures, Eddy proceeds to silence him by pointing out that confusion is yet another symptom. After this, Edd is subjected to several physical tests by Ed, most of which make no sense and seem to have been made up on the spot.
After these tests, Edd fears the worst, as he's obviously expiring. Eddy then asks if anybody has tried to kick him; upon receiving a "no", he says that Edd is in the clear, as people trying to kick the disease-bearer is the final symptom while surreptitiously slapping a "Kick Me" sign on Edd's back. Edd is relieved by this news until Eddy kicks him, sending him skyward. Eddy then fakes shock, saying that he thought Edd didn't have the final symptom. Worried, Edd asks Dr. Ed how long he has to live and Ed, not being the brightest bulb in the box, suggests that Edd has until lunch. Edd nearly faints when he hears this, but is revived somewhat when Eddy slips a piece of paper and a pencil into his hand and tells him to write. Edd asks if he's supposed to write a sonnet on the beauty of life, but as usual, Eddy is thinking only of himself, and tells Edd to write out his will, and leave something nice to him. Ed asks for Edd's hat, and this is the final straw, as he goes off wailing about how he is not long for this world. Eddy bursts into laughter, but Ed starts to cry, having been caught up in the charade; Ed's tears quickly turn to smiles when Eddy reminds him that they're pranking Edd, however.
Edd wanders around the cul-de-sac and sees most of the kids coming down the lane, heading for the beach. They invite Edd to join them but, depressed, he can only cry about how little time he has left. He has taken Eddy's advice, however, and is giving his stuff away. To Rolf he bequeaths his microscope, which Rolf mistakes for a peanut-smasher, and to Jonny he gives his remote control. Edd then turns to Nazz and bemoans the fact that there are so many things left unsaid between them; when Nazz asks what they are, however, he just turns away, weeping. This exposes his back and the "Kick Me" sign to Jimmy, who swiftly walks up and dispenses a light kick, giggling all the way. Jimmy's merriment soon turns to confusion, however, as Edd wails about the horror of Lackadaisycathro Disease–only for Nazz to peel the sticky note from his back and show it to him. As Edd catches on to what his friends did to him, the other kids walk off, ready to head for the beach.
Ed and Eddy are still having fun at Kevin's expense by building a brick wall around his house, when Edd comes back, steaming with rage and demanding to know why they would do something so evil to him. Eddy tries to brush him off, but is soon distracted by the specter of Kevin on the outside now. Kevin explains that he got off earlier for good behavior, and Eddy first grovels, then runs away with Ed and hides in his house and locks the door. Kevin growls as Ed and Eddy happily dancing around inside, having escaped his rage again, but is soon distracted by Edd, who happens to have Eddy's spare house key and is only too glad to "misplace" it somewhere that Kevin can find it. Kevin is all too willing to play along, and Ed and Eddy are soon on the receiving end of a thrashing that Edd deems part of "Kevin's Justified Pummel Disorder".
Ed and Eddy's pile of toilet paper rolls disappears when Jimmy walks by.
Ed was seen with four toes. Typically, all the characters have three toes.
Similarly, as Edd gives his possessions away to the kids, Nazz and Sarah can be seen with four toes.
Sarah only appears in one scene, wearing a yellow swimsuit. When the camera pans to her, she is wearing her normal pink shirt.
When Jimmy kicks Edd's buttocks, Edd has both his shoes on. In a previous scene, Ed ate Edd's left shoe, and Edd is seen without it for the rest of the episode.
When Edd confronts Eddy about the "kick me" sign planted on him, he's holding it from the top with his left hand. When the camera angle changes to face Edd, he's holding it from the bottom with his right hand.
Ed breaks the fourth wall by saying, "That's some good TV right there."
The disease name (Lackadaisycathro Disease) is a play on the word "lackadaisical", meaning to be lethargic and without vigor. It also combines the last name of Ken Cathro, one of the Creators on the show.