We investigated the extent to which estrogen receptor (ER) and progesterone receptor (PR) status results from a centralized pathology laboratory agree with ER and PR results from community pathology laboratories reported to two Surveillance, Epidemiology and End Results (SEER) registries (Los Angeles County and Detroit) and whether statistical estimates for the association between reproductive factors and breast cancer receptor subtypes differ by the source of data. The agreement between the centralized laboratory and SEER registry classifications was substantial for ER (kappa = 0.70) and nearly so for PR status (kappa = 0.60). Among the four subtypes defined by joint ER and PR status, the agreement between the two sources was substantial for the two major breast cancer subtypes (ER-/PR-, kappa = 0.69; ER+/PR+, kappa = 0.62) and poor for the two rarer subtypes (ER+/PR-, kappa = 0.30; ER-/PR+, kappa = 0.05). Estimates for the association between reproductive factors (number of full-term pregnancies, age at first full-term pregnancy, and duration of breastfeeding) and the two major subtypes (ER+/PR+ and ER-/PR-) differed minimally between the two sources of data. For example, parous women with at least four full-term pregnancies had 40% lower risk for ER+/PR+ breast cancer than women who had never been pregnant [centralized laboratory, odds ratio, 0.60 (95% confidence interval, 0.39-0.92); SEER, odds ratio, 0.57 (95% confidence interval, 0.38-0.85)]; no association was observed for ER-/PR- breast cancer (both P(trend) > 0.30). Our results suggest that conclusions based on SEER registry data are reasonably reliable for ER+/PR+ and ER-/PR- subtypes.