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Cultural factors are important in birth seasonality in a village where other influencing factors such as temperature and humidity are relatively constant. The Western Abelam people have a system of ritual beliefs, involving the growth of ceremonial yams, which encourages a six-month period of sexual abstinence. Since birth control methods were not practiced, seasonal patterns in conceptions and births were hypothesized and tested using demographic data from one village. The seasonal distribution of known birth months of surviving children differed significantly from random (p < .02). As predicted by ethnographic evidence, results for children of yam growers were significant (p <.005) while birth season of children of non yam growers did not deviate significantly from the expected. The relationship among seasonal birth patterns and cultural, climatological and nutritional variables are examined. Results suggest the primary importance of cultural factors in Western Abelam birth seasonality.