The subjects consisted of 650 children (American white 245, Chinese 202, Japanese 203) from five to twelve years old, who came to the Department of Growth & Development, University of California, San Francisco. Mandibular first molar development was determined by inspecting panoramic radiographs and assigning a rating according to Kullman's method, which classifies tooth formation into seven stages according to growth and development. The samples in each age-stage were evaluated by their means values. Tooth formation was significantly more advanced in the American white children than in the Chinese or Japanese at all stages. The significance of the difference between Chinese and Japanese children was not identified. Tooth formation was shown to be highly correlated with chronological age, with a coefficient of more than 0.7 in all racial groups.