A 23-month-old girl with a history of mild atopic dermatitis presented for evaluation of a rash. The rash first appeared 3 days previously on her arms and legs and progressed rapidly to also involve her face and torso. A transient fever was reported when the rash first appeared. There was no history of cough, rhinorrhea, nausea, vomiting, abdominal pain, diarrhea, or arthralgias. She was not receiving any medications. She attended day care, where at least 1 other child reportedly had been ill with fever and rash.