Several reports have noted an association between the use of tamoxifen in breast cancer patients and the subsequent development of endometrial carcinoma. Magriples et al. (J. Clin. Oncol. 11, 485-490, 1993) recently reported that 67% of uterine cancers that developed in 15 breast cancer patients on tamoxifen had high-grade lesions or high-risk histologies, compared to 24% of those developing in 38 breast cancer patients not receiving tamoxifen. To confirm these results, we conducted a retrospective review of 73 patients with a history of breast cancer who subsequently developed uterine cancer and underwent surgery at our institution. Twenty-three (32%) had received tamoxifen for at least 1 year, with a median duration of use of 4.5 years, while 50 (68%) did not receive tamoxifen. The median interval between diagnosis of breast and corpus cancer was less in the group that received tamoxifen than in the group that did not (4.6 vs 6.7 years), but this was not statistically significant. Seventy-four percent of the corpus cancers in the tamoxifen group were adenocarcinomas, while 26% were considered high-risk histologies, which was identical to the findings for the group that did not receive tamoxifen. The distribution by FIGO stage was I, 15 (65%); II, 2 (9%); III, 5 (22%); and IV, 1 (4%) for the tamoxifen group, and I, 37 (74%); II, 1 (2%); III, 8 (16%); IV, 3 (6%); and unstaged, 1 (2%) for the group not receiving tamoxifen (P = NS). For patients with endometrial adenocarcinoma, 23% of the tamoxifen group had grade 3 lesions, compared with 19% of the no tamoxifen group (P = NS). Our review of corpus cancers developing in breast cancer patients demonstrated no significant difference in stage, grade, or histologic subtype based on tamoxifen use.