With regard to the development of chronic disease and the inprovement in adult life expectancy there is a longstanding debate on the relative importance of factors operating in early life compared with genetic charactersistics and environmental factors in later life. Early cohort analysis revelaed that, up until 1925, year of birth was more important than year of death in the prediction of mortality risk. This lent support to the developing child welfare services as social reformers attributed the ‘generation effect’ to the long-term effects of the early environment, although others thought genetic characteristics played a part. Intrest in the early environment dissipated after the Secong World War when mortality predictions based on early cohort anlysis failed to be fulfilled; instead adult lifestyles became the focus of attention. In the last ten years there has been a resurgence of intrest in the influence of the early environment on chronic diseases. In contrast to the earlier work, recent theories stress the importance of the prenatal period rather than childhood and the nature of the casual links are less self-evident. Furthermore they provide a direct challenge to current policies focussing on adult lifestyle. This paper charts the early development, disappeances and re-emergence of theories relating mortality risk to early experience, and compares the empirical investigations carried out in each period in terms of their content, their contribution to epidemiological research, the response of the scientific community, and their timing in relation to the wider policy debate.