We measured stable nitrogen isotope ratios in bone collagen of 60 individuals from the early Neolithic (9th–8th millennium Cal. BC) sites of Çayönü Tepesi and Aşıklı Höyük. Our aim was to identify the duration of exclusive breastfeeding (EBF), compare this with juvenile mortality at each site, and assess whether there was a relationship between them. The isotope analysis suggests that weaning commenced at about 1 year at Aşıklı Höyük and around 2 years at Çayönü Tepesi. The mortality data show equal numbers of infant deaths up to 24 months; however, after 24 months, the mortality rate increases at Çayönü Tepesi, and a Student's t-test confirms a significant difference in infant mortality between the sites. Weaning foods prepared in the early Neolithic from agricultural crops would have had low-iron content, poor nutritional value, and would have been prepared in nonsterilized containers. Therefore, later weaned infants in early Neolithic farming settlements, although capable of some immunological response, were probably undernourished putting them at a disadvantage when encountering bacteria in their weaning food. Our results suggest that infant feeding regimes that introduced infants to weaning foods in the first year of life may have had a positive effect on their survival. Am J Phys Anthropol, 2010. © 2010 Wiley-Liss, Inc.