The classification of onychomycosis, infection of the nail apparatus caused by fungi, has changed over time with the recognition of new pathways of nail infection, new organisms, and new variations in the appearance of diseased infected nail. Taking into account published descriptions of nail morphology in fungal infection, the following forms of onychomycosis are recognized: distal and lateral subungual, superficial, endonyx, proximal subungual, mixed, totally dystrophic, and secondary onychomycosis. These can be subdivided, where appropriate, by color and pattern of nail plate change. The purpose of the revised classification is to provide a framework to assist selection of treatment, estimate prognosis, and evaluate new diagnostic methods.