Utilizing the 'Metropolitan' database, which provides unique longitudinal data on a cohort of 15,000 individuals born in Stockholm in 1953, the paper tests various hypotheses on how conditions in childhood and social upbringing influence sickness absence in adulthood. The hypotheses were derived from different perspectives within the social sciences. The findings suggest that the effects of social background are transmitted via several mechanisms, and that it is useful to see some of the competing hypotheses on social class and health-related phenomena as complementary rather than contradictory. However, the results also suggest that both 'the culture of poverty hypothesis' and the 'biological imprint hypothesis' should be rejected. Because effects of social background are mediated by career variables such as school performance, educational level and current socio-economic status, the results support the 'unfavourable life career hypothesis'. In addition to these effects, an influence of being brought up in a family with serious domestic problems is found. This is congruent with 'the social imprint hypothesis', that childhood conditions may have lasting effects on conditions and behaviours in adult life, irrespective of later exposure.