The purpose of this study was to examine the risk of premenopausal breast cancer for women in relation to childbearing recency and whether this association differs by breast-feeding history and/or the amount of weight gained during pregnancy. This analysis was based on data from a population-based case-control study composed of 1,706 incident cases of invasive breast cancer and 1,756 population controls from Wisconsin, New Hampshire, and Massachusetts. In a telephone interview conducted from 1996 to 2001, information was gathered on established breast cancer risk factors, as well as reproductive history, including amount of weight gained during the last full-term pregnancy and whether the child was breast-fed. Unconditional logistic regression was used to estimate odds ratios and Wald 95% confidence intervals for the risk of breast cancer. When compared with nulliparous women, women that had given birth within the past 5 years before breast cancer diagnosis in the cases or a comparable period in controls had a nonsignificant 35% increased risk of invasive breast cancer (odds ratio, 1.35; 95% confidence interval, 0.90-2.04), adjusting for age and known breast cancer risk factors (Ptrend = 0.14). We did not find a significant interaction with breast-feeding (Pinteraction = 0.30) or pregnancy weight gain (Pinteraction = 0.09).