This paper examines, theoretically and empirically, the impact of reproductive externalities on fertility behaviour in Kenya. We examine this issue by identifying structural forms of social interaction operating across individuals belonging to different ethnic groups on the number of children ever born. We use the 1998 Demographic and Health Survey, and meteorological data on Kenya, to examine whether social interactions effects are important over and above an individual's characteristics in order to explain variations in fertility. In so doing, we conclude that social interactions are very important for the fertility behaviour of different ethnic groups in Kenya.