Varicella may be associated with serious complications including encephalitis, Reye's syndrome, and drug toxicity. In this case, a 19-month-old child with varicella was brought to the family practice clinic by her parents when she began behaving abnormally. At the time of presentation the child exhibited dilated pupils, ataxia, urinary retention, and facial grimacing. The child's parents had treated her with acetaminophen, diphenhydramine syrup, colloidal oatmeal baths, and frequent applications of Caladryl lotion. The results of her immediate laboratory tests were within normal limits, and she was admitted to the hospital for observation. She recovered without therapeutic intervention. Although not available at the time of admission to the hospital, her diphenhydramine serum level was 1948 ng/mL. Diphenhydramine levels above 100 ng/mL have been associated with toxicity.