The positive effects of dispositional optimism on mental and physical health are well documented, but little is known about its developmental origins. The present population-based longitudinal study of young adults (n = 8673) examined predictors of optimism that were related to early childhood family conditions, school achievement in middle childhood, education, and work status in early adulthood. As theoretical starting points, previous research on other related positive psychological constructs, previous research on depression, and life span research were used. The results showed that the wantedness of the child, the father's socioeconomic status and changes in it, school achievement, vocational education and work history predicted significantly optimism at 31 years. A good financial situation and being married were strongly associated with optimism at 31 years.