Despite the recent and rapid worldwide rise in body mass index (BMI), little empirical research outside the developed world has systematically considered the role of cohorts in inaugurating emergent biomorphic disparities. This study integrates aspects of the life course perspective (attention to age- and cohort-level influences) with fundamental cause theory to investigate how BMI differences have unfurled in the Chinese population. We analyze growth-curve models of adults in the China Health and Nutrition Survey. The results indicate that more recent cohorts have higher levels of BMI and, among women, experience a steeper rate of age-related BMI growth. Moreover, biomorphic change has unfolded in complex ways related to social conditions across successive cohorts. The most pronounced changes are observed among women, who demonstrate an emerging disparity in BMI levels on the basis of education and urban versus rural residence. (Contains 2 tables, 2 figures and 6 notes.)