This study was conducted to investigate the efficacy of oral terbinafine with and without aggressive debridement for the treatment of toenail onychomycosis. Onychomycosis patients aged 18 to 75 years received 12 weeks of terbinafine, 250 mg/day, alone (n = 255) or with aggressive debridement (n = 249). Both groups showed marked improvement from baseline at all time points. At week 48, complete, mycologic, and clinical cure rates were higher in the terbinafine plus debridement group compared with the terbinafine alone group, although significance was reached only for clinical cure (59.8% versus 51.4%; P = .023). Although approximately 39% of the patients received at least one antidiabetic, antihypertensive, or cholesterol-lowering agent concomitantly, including statins, the incidence of treatment-emergent adverse events was low and the adverse events were generally mild to moderate in severity. No clinically significant changes in liver transaminase levels were observed 6 weeks after treatment or after 12 weeks in those tested. These results support the well-established safety and efficacy of terbinafine for treatment of onychomycosis.