We investigated the risk associated with variants in three genes involved in estrogen biosynthesis, CYP11A1, CYP17A1, and CYP19A1, in the population-based case–control study of Estrogen, Diet, Genetics, and Endometrial Cancer. This study was conducted in New Jersey in 2001–2006 with 417 cases and 402 controls. For CYP11A1, there was no association between the number of [TTTTA] n repeats (D15S520) and risk. For CYP17A1, risk was somewhat lower among women with the C/C genotype at T-34C (rs743572) (adjusted OR = 0.65, 95% CI 0.41–1.02). For CYP19A1, risk was lower among women homozygous for the 3-bp deletion (rs11575899) in exon 4 (adjusted OR = 0.44, 95% CI 0.26–0.76), while the number of [TTTA] n repeats was not significantly related to risk: the adjusted OR for n = 7/7 repeats versus n > 7/>7 repeats was 0.81 (95% CI 0.54–1.23). In stratified analyses, results for CYP19A1 were stronger among women with higher (≥27.4) body mass index: for the homozygous deletion, OR = 0.30 (95% CI 0.15–0.62); for the n = 7/7 genotype, OR = 0.49 (95% CI 0.26–0.93). The interaction between the n = 7/7 genotype and BMI was statistically significant (p = 0.01). The insertion/deletion variant in CYP19A1 appears to be related to risk of endometrial cancer; risk associated with variants in this gene may vary according to BMI.