We examined the association between life course body weight percentile trajectories and risk for preterm delivery (PTD). Data about women’s weight at birth, age 18, and before pregnancy were obtained by retrospective self-report in a cohort of 1410 black women in metropolitan Detroit. Growth mixture models were used to categorize women with similar weight percentile trajectories across these time points. Log-Poisson models were used to examine the association between the trajectory groups and PTD. Four trajectory groups with different beginning and endpoints of their weight percentiles (high-high, high-low, low-high and low-low) best fit the data. The groups with the highest prevalence of PTD were those that started low (low-high, 21%; low-low, 18%). The low-high group had a higher prevalence of PTD than the high-high trajectory group in unadjusted models (prevalence ratio=1.49 [95% confidence interval (CI) 1.11, 2.00]). The association became not significant after adjusting for maternal age at delivery, income, diabetes and hypertension. When compared with the high-high trajectory group, the low-low trajectory seemed to also have a higher prevalence of PTD after adjusting for maternal age at delivery, income, diabetes and hypertension (prevalence ratio=1.35 [95% CI 1.00, 1.83]). Results suggest that a woman’s risk for PTD is influenced by her body weight trajectory across the life course.