OBJECTIVES: This study investigated timing and duration effects of socioeconomic status (SES) on self-rated health at 33 years of age and established whether health risks are modified by changing SES and whether cumulative SES operates through education. METHODS: Data were from the 1958 British birth cohort. Occupational class at birth and at 16, 23, and 33 years of age was used to generate a lifetime SES score. RESULTS: At 33 years of age, 12% of men and women reported poor health. SES at birth and at 16, 23, and 33 years of age was significantly associated with poor health: all ages except 16 years in men made an additional contribution to the prediction of poor health. No large differences in effect sizes emerged, suggesting that timing was not a major factor. Odds of poor health increased by 15% (men) and 18% (women) with a 1-unit increase in the lifetime SES score. Strong effects of lifetime SES persisted after adjustment for education level. CONCLUSIONS: SES from birth to 33 years of age had a cumulative effect on poor health in early adulthood. This highlights the importance of duration of exposure to socioeconomic conditions for adult health.