Purpose: Socioeconomic position (SEP) has been shown to be related to obesity and weight gain, especially among women. It is unclear how different measures of socioeconomic position may impact weight gain over long periods of time, and whether the effect of different measures vary by gender and age group. We examined the effect of childhood socioeconomic position, education, occupation, and log household income on a measure of weight gain using individual growth mixed regression models and Alameda County Study data collected over thirty four years(1965-1999). Methods: Analyses were performed in four groups stratified by gender and age at baseline: women, 17-30 years (n = 945) and 31-40 years (n = 712); men, 17-30 years (n = 766) and 31-40 years (n = 608). Results: Low childhood SEP was associated with increased weight gain among women 17-30 (0.13 kg/year, p < 0.001). Low educational status was associated with increased weight gain among women 17-30 (0.14 kg/year, p = 0.030), 31-40 (0.14 kg/year, p = 0.014), and men 17-30 (0.20 kg/year, p = 0.001). Conclusion: Log household income was inversely associated with weight gain among men 31-40 (-0.10 kg/yr, p = 0.16). Long-term weight gain in adulthood is associated with childhood SEP and education in women and education and income in men.