About 20% of the US population between the ages of 40 and 60 years have fungal nail disease, or onychomycosis. The incidence of this infection is increasing worldwide. Most cases of onychomycosis in the United States are caused by dermatophytes, but nondermatophyte fungi (molds or yeasts) may also be causative agents. To confirm the diagnosis of onychomycosis, a potassium hydroxide examination should be performed. A culture is necessary to determine the fungal pathogen and to aid in selecting appropriate therapy. Worldwide, fluconazole (not yet approved in the United States for onychomycosis), itraconazole, and oral terbinafine have superseded griseofulvin and ketoconazole as the agents of choice in treating onychomycosis. These newer systemic compounds have higher cure rates and cause fewer side effects than traditional agents. Intermittent dosing with itraconazole (3 or 4 one-week pulses of 200 or 400 mg daily) is the latest advance in the treatment of onychomycosis. This regimen has been found to be at least as safe and effective as short-term continuous therapy, yet more flexible, convenient, and economical.