Onychomycosis is a frequent nail disease caused by dermatophytes, yeasts, and nondermatophyte molds. Trichophyton rubrum, T mentagrophytes, and Epidermophyton floccosum are the most common etiologic agents worldwide. Candida spp are the most frequent among the yeasts. Diagnosis is corroborated by direct microscopic examination, culture, and histomycology with periodic acid-Schiff stain. Other new methods of diagnosis are discussed. Treatment is based on oral antifungals: terbinafine, itraconazole, and fluconazole, including other emerging triazole drugs. Therapeutic outcome with ciclopirox and amorolfine lacquers alone and combined with systemic therapy are also reviewed, as well as the new nail enhancers and physical and chemical removal of the diseased nails.