The focus of the study is on the importance of early optimism for adult subjective well-being (SWB). Only females were studied. Data from age 13 and age 43 were taken from the Swedish longitudinal research program Individual Development and Adaptation (IDA, Magnusson, 1988). We investigated the longitudinal relationship between early optimism and optimism at 43, its mediation via positive and negative affect measured at age 43, and finally the "effect" on global life satisfaction at age 43. For this purpose, structural equation methodology was used and the fit indices were compared among three extended cognitive-affective models, based on Chang is work (Chang, 2002). The best fitting model suggests that early optimism influences optimism at a middle age, which in its turn has both a direct influence on glogal life satisfaction and an indirect influence via the negative affect dimension. In further analyses we studied the importance of early optimism for adult SWB in relation to hte importance of a number of other factors measured in adolescence. Optimism at age 13 was the only factor the was consistently related to women's SWB at age 43.