Background: Onychomycosis is the most frequent cause of nail disease and represents 30% of all mycotic infections of the skin. Objective: Our purpose was to compare the effectiveness and tolerability of intermittent dosing of itraconazole ('pulse therapy') with placebo in fingernail onychomycosis. Methods: Seventy-three patients with clinically and mycologically diagnosed fingernail onychomycosis were randomly selected to receive itraconazole, 200 mg twice daily, or placebo for the first week of each month for 2 consecutive months; patients were observed for 19 weeks. Seventy-one patients received the study medication and were included in the safety analysis. Efficacy of treatment was evaluated in 46 patients. Results: A significantly greater proportion of itraconazole-treated patients than placebo-treated patients achieved clinical success (77% vs 0%), mycologic success (73% vs 13%), and overall success (68% vs 0%). No itraconazole-treated patient had a clinical or mycologic relapse during the follow-up period. Ten itraconazole-treated patients (28%) and nine placebo-treated patients (26%) had adverse events. Three patients discontinued treatment for safety reasons. Conclusion: Pulse therapy with itraconazole for 2 consecutive months produces significantly greater clinical, mycologic, and overall success than placebo. Short-term itraconazole pulse therapy for fingernail onychomycosis is effective and well tolerated.