A statistical study of 240 patients with nevus of Ota was carried out. The onset was before 1 year of age in 119 and after the age of 2 in 121. Onset between the ages of 1 and 11 years is distinctly rare. In type 3, 77% of the cases began before 1 year of age. Color is influenced by fatigue, menstruation, insomnia, and weather. The association of ocular and buccal melanosis and of Mongolian spots and blue nevus was discussed. Among 207 families, there were two familial incidences and 15 patients whose parents were related, but heredity was not suggested. No malignant change was observed. Clinical features in childhood, in adolescence, and in old age were described. Spontaneous regression did not occur. The clinical course in childhood was followed, and subtle changes of extent, tone, and intensity of color were observed. It was concluded that before 1 year of age pigmentation increases, and after the age of 2 it may show a regression.