Nail lesions can be related to a number of disease states. These may be intrinsic to the nail, caused by infection, or reflect systemic disease. Careful history and examination often is necessary for accurate diagnosis. Anatomy and gross changes of the nail are reviewed. The diagnosis and treatment of disease process such as psoriasis, lichen planus, paronychia, onychomycosis, myxoid cysts, and pincer nails are reviewed.