This section of Pediatrics in Review reminds clinicians of those conditions that can present in a misleading fashion and require suspicion for early diagnosis. Emphasis has been placed on conditions in which early diagnosis is important and that the general pediatrician might be expected to encounter, at least once in a while. The reader is encouraged to write possible diagnoses for each case before turning to the discussion, which is on the following page. We invite readers to contribute case presentations and discussions. Case 1 Presentation A 10-year-old boy is brought to your office in late spring because of an erythematous rash on his arms and legs that has been present for 4 days and because he is having joint pains. The rash first appeared after the boy had been playing outdoors for several hours in the sun. He did have a new commercial sunblock lotion applied to his skin before going outdoors. His father is concerned because even though the rash is less pronounced, his son has been experiencing stiff and painful knees and ankles upon awakening for the past 2 days. The joint discomfort improves with movement during the day. The boy has had no other symptoms and has been free of fever.