OBJECTIVE To determine whether acetaminophen affects the duration or severity of childhood varicella. METHODS Randomized, double-blind, placebo-controlled trial. METHODS Office- and hospital-based pediatric practices. METHODS Seventy-two children between 1 and 12 years of age entered the study. One child was withdrawn because of high fever, and three children did not complete the study; 31 received placebo and 37 received acetaminophen. METHODS Acetaminophen, 10 mg/kg/dose, was given at 8 AM, 12 PM, 4 PM, and 8 PM for 4 days. Placebo was given to the control group. Itching, appetite, activity, and overall condition were measured for 6 days. The time to last vesicle formation, time to total scabbing, and time to total healing were measured until complete resolution of the exanthem. RESULTS The following results were better in the placebo group (p less than .05): time to total scabbing 5.6 days (SD 2.5) versus 6.7 days (SD 2.3) in the acetaminophen group, and itching on day 4 in the placebo group (symptom score 2.9 (SD 0.20) vs 2.2 (SD 0.26]. Activity was better in the acetaminophen group on day 2 (3.13 (SD 0.23) vs 2.82 (SD 0.24]. CONCLUSIONS These results provide evidence that acetaminophen does not alleviate symptoms in children with varicella and may prolong illness.