Important information on demography, epidemiology, inter-population differences in growth, infant burial practices, and social aspects of the community can be gleaned from the study of perinatal bones. The increasing number of perinates unearthed from prehistoric sites in Southeast Asia provides a rare opportunity to investigate these issues. The high number of full-term infants represented at the site of Khok Phanom Di in Central Thailand (4000–3500 b.p. ) remains an enigma. This is an important issue for bioarchaeologists as infant mortality patterns are sensitive barometers of the health and fertility of a population. This study investigated the perinatal age distributions of several chronologically spread sites in prehistoric Southeast Asia with differing subsistence modes and evidence of social complexity. Results show that the age distribution in the collection from Khok Phanom Di is different from the other skeletal samples, with a comparatively higher number of full-term perinates represented. Explanations including infanticide, issues of health and disease, and infant burial practices are considered. It seems likely that the age distribution results from different burial rites of pre-term infants as a consequence of social and cultural differences between Khok Phanom Di and the other sites. This study emphasizes the important contribution bioarchaeological research and the comparative study of infant burial rites can make in understanding aspects of social change in prehistoric communities.