The safety and efficacy of 0.03% and 0.1% tacrolimus ointment for the treatment of atopic dermatitis were evaluated in a 12-week, randomized, double-blind, vehicle-controlled study of 351 children 2 to 15 years of age with moderate to severe atopic dermatitis. The mean age of patients was 6.1 years. A total of 61.5% of patients had severe atopic dermatitis at baseline. The mean percentage of body surface area affected was 47.7%, and 83.5% of patients were affected on the head and/or neck. Significantly more patients (P<.001) achieved clinical improvement of 90% or better with 0.03% or 0.1% tacrolimus ointment compared with vehicle. Significant improvements in the signs and symptoms of atopic dermatitis, percent body surface area affected, and the patient's assessment of pruritus were also observed early in treatment and were maintained throughout the study. Adverse events with a statistically significantly greater incidence in the 0.03% tacrolimus ointment treatment group compared with vehicle were limited to the sensation of skin burning, pruritus, varicella, and vesiculobullous rash ("blisters"). Varicella and vesiculobullous rash occurred at a low incidence (<5%). No adverse event occurred at a statistically higher incidence in the 0.1% tacrolimus ointment-treated group compared with vehicle. Tacrolimus ointment was equally safe for younger (2-6 years) and older (7-15 years) children. Both tacrolimus ointment concentrations (0.03% and 0.1%) were safe and significantly more effective than vehicle for the treatment of atopic dermatitis in children.