Monkey digits were used experimentally to demonstrate the pathologic anatomy of nail deformities and the results of treatment using full and partial thickness nail matrix grafts. Seventy-five human nail deformities were evaluated and treated. In both the experimental and clinical groups, microscopic hypertrophy of the superficial epithelial elements underlying the deformed nail existed. A follow-up of treatment of nail deformities indicated that nail matrix grafts, both full and partial thickness, are beneficial when the defect involves the sterile matrix and the proximal nail fold.