METHODS The fungicidal mode of action of terbinafine should make it feasible to reduce treatment duration in onychomycosis. For this reason, a randomized, double-blind study in 195 patients with severe dermatophyte infections of the toenails was performed comparing a 24-week treatment with terbinafine (250 mg/d) with a 48-week treatment with micronized griseofulvin (1000 mg/d). RESULTS After 48 weeks, effective treatment was achieved in 67% of the patients treated with terbinafine and in 56% of those treated with griseofulvin (two-tailed P = .120). At a follow-up visit 24 weeks later, cure rates had decreased to 60% in the terbinafine group and to 39% in the griseofulvin group (two-tailed P = .006). At the same time, the mycological cure rate was 81% with terbinafine and 62% with griseofulvin (two-tailed P = .02). CONCLUSIONS This study has demonstrated the longterm therapeutic superiority of terbinafine to high-dose griseofulvin in the treatment of toenail mycosis. Furthermore, with the new antifungal terbinafine, treatment is no longer necessary until all affected nail material has grown out.