Developmental exposure to polychlorinated biphenyls (PCBs) disrupts reproduction in animals. Human data are lacking. We measured PCBs in preserved mothers’ serum samples collected during 1960-1963, 1-3 days after their daughters’ birth. We recorded time to pregnancy (TTP) in 289 daughters 28-31 years later. PCB congeners 187, 156, and 99 in mother’s serum were associated with longer TTP in their daughters while PCB congeners 105, 138 and 183 were associated shorter TTP. Probability of pregnancy fell by 38% (95% CI 17-53%) and infertility was higher (30% not pregnant after 13 cycles versus 11% not pregnant after 13 cycles) among women whose mothers had a higher proportion of PCB congeners associated with longer TTP (75th percentile versus 25th percentile). This study demonstrates, for the first time, that developmental exposure to PCBs may disrupt pregnancy in humans.