Comparisons were made of the findings of fifty cross-cultural studies of psychomotor development, from birth to two years, of contemporary groups of infants on five continents. The effects of ethnicity, amount and type of caretaker stimulation, and nutritional status were discussed. African infants showed the greatest early acceleration, Caucasian infants the least, while Latin American and Asian infants ranked intermediate. Within each ethnic group, "traditionally" reared, rural infants showed greater motor acceleration than "Westernized, " urban infants in the first six to twelve months, and a greater decline, after weaning, in adaptive and language development, in the second year. Within both traditional and Westernized samples of the same ethnic groups, infants with higher birthweight were more accelerated.