The effect of oral contraceptive (OC) use was examined among parous breast cancer cases diagnosed at less than or equal to 45 years of age, and in two different general population control groups of parous women. The primary analysis compared 278 cases with 520 controls. In the secondary analysis, a subgroup of 190 cases were compared with 190 controls from another reference group. In both analyses, ever use of OC, duration of OC use, and OC use prior to first pregnancy showed no significant association with breast cancer risk. Also in both analyses, in women with prior benign breast disease OC use increased the risk of breast cancer, although this finding was statistically significant only in the larger group used in the primary analysis.