This study describes the shifting age and sex patterns of populations across rural and urban sectors in sub‑Saharan Africa from 1980 to 2015. It examines the relationship between the slowdown in urbanization and rural and urban age structure gaps, sex composition and dependency ratios. Findings show that rural-urban migration of young adults plays a key role in explaining dependency ratios and sex compositional gaps in rural and urban areas. Results also highlight the value of taking into account local age and sex structures to better prepare for the demographic dividend and other consequences of demographic shifts in sub-Saharan Africa.