Background: Tinea corporis and tinea cruris are usually treated with a topical antifungal agent unless the infection is unresponsive, involves an extensive area, is chronic, or is in a difficult-to-access area. In these cases oral antifungals are frequently used. Objective: This double-blind study was undertaken to determine whether a 2-week course of oral itraconazole would produce statistically significant clinical and mycologic improvement in the treatment of tinea corporis, tinea cruris, or both, over the results obtained with placebo. A second objective was to determine the safety of itraconazole, through routine measurements of serum chemistry profiles. Methods: Sixty-seven patients were entered into a double-blind, multicenter study to compare the clinical and mycologic effects of itraconazole, 100 mg daily (45 patients), and placebo (22 patients) on tinea corporis and/or tinea cruris. The duration of treatment was 2 weeks. The investigators assessed signs and symptoms and performed a potassium hydroxide examination and culture at baseline, at termination of therapy, and 2 weeks after completion of treatment. Results: Twenty-two (96%) of 23 evaluable patients in the itraconazole group had healed or markedly improved lesions, as compared with 5 of 13 (39%) in the placebo group (p less than or equal to 0.01). Similarly, the condition in 13 of 23 patients (57%) in the itraconazole group was mycologically cleared at the end of treatment whereas this result occurred in only 2 (17%) of 12 patients in the placebo group (p =0.02). The prevalence of adverse side effects was lower for the itraconazole-treated group (20%) than for the placebo-treated group (36%). Conclusion: Itraconazole 100 mg once daily is an effective agent for the treatment of tinea cruris and tinea corporis.