This paper reviews trends in rural/urban under-5 mortality differentials in Sub-Saharan Africa in historical perspective, with particular attention to the case of Kenya. The rural/urban mortality gap has narrowed within the last half-century, but while this was largely due to rapidly falling rural infant and childhood mortality over most of the period, in recent years it has been due primarily to a stalling and even upturn in urban under-5 mortality as urban economic and environmental conditions have sharply deteriorated in rapidly growing cities. Policy attention and resources need to be directed to large urban areas to prevent further deterioration of urban mortality and associated health conditions.