Purpose – The objective is to determine the influence of economic and social/cultural factors on family size and child gender preferences in rural Kenya and to draw public policy implications from the results. This is an important matter because the fertility rate in Kenya is high; higher than in most developing countries. It is especially high in rural areas. This may be an impediment to Kenya's development. Design/methodology/approach – First relevant economic literature is reviewed to identify factors that economists and others claim are important influences on family size. Then follows a case study of families in the Nyeri district of Kenya. Data are obtained from a random sample of households in this district using a semi-structured questionnaire in direct interviews. The survey results are summarised and then analysed using Tobit analysis and least squares regression. Findings – Both economic and social/cultural factors are found to be important influences on family size. For example, preference for male children has an important positive influence on family size in the Nyeri district. Women are found to prefer male offspring to daughters, possibly because they are afraid of being disinherited if they do not produce a male heir for their husbands. Research limitations/implications – Support for the conclusions reached could be strengthened or further assessed by increasing the sample size in the Nyeri district and be conducting similar surveys in other rural districts of Kenya. Practical implications – Introducing social security systems in Kenya to assist the elderly and the infirm would reduce the need for Kenyan women to have many children as security and women should be granted greater inheritance rights, especially to land. Furthermore, education of women should be promoted as a way to reduce family size. Originality/value – This paper reinforces the view that both economic and social/cultural factors must be considered simultaneously when examining determinants of the number of children in a family and child gender preference.