Summary Because of current interest in the child survival hypothesis, we have reviewed available evidence bearing upon the relationships of infant and child mortality to fertility and contraceptive behaviour. The evidence is drawn from time series data for local and national vital events, from special in-depth studies of the infant mortality-fertility relationships in family formation, and from service statistics from health and family planning programmes. As a result of this review, we suggest five clarifications which should be made in redefining the child survival hypothesis and assessing its potential programme implications. The child survival hypothesis states that improved child survival will contribute to increased family planning motivation and consequent fertility decline. The evidence presented here suggests that the effect is not automatic and probably not a necessary pre-condition for fertility decline. There is certainly not a reflexive one-to-one replacement, but a partial effect may still be important. In the clearly demonstrated reduction in inter-pregnancy intervals after a child death, the major component is undoubtedly the removal of the biological protection of lactational amenorrhoea. A separate but somewhat smaller effect has been demonstrated in situations where lactation did not seem to have been the explanation. It is expected that increased child survival will contribute to fertility decline mainly in countries experiencing rapid mortality decline and population growth. The replacement of children who die is probably not so much 'volitional' as a result of alterations in sub-conscious expectations. It is apparent that in traditional agrarian populations, few direct and manipulable means of influencing motivation for fertility limitation are available, and, therefore, it must be stressed that integrated health and family planning programmes do provide opportunities for immediate programme development. By making parents aware of improved changes of survival through health services in which they develop confidence, the spontaneous linkages between mortality and fertility can presumably be reinforced. Family planning services must be provided as an essential initial step in programme development, but they can be made more effective, as well as politically more acceptable if appropriately integrated with maternal and child health and nutrition services.