This cross-sectional study of 556 postmenopausal women with early-stage breast cancer treated with aromatase inhibitors found that high fat body mass was associated with a numerically but not significantly lower proportion of vertebral fractures in aromatase inhibitor–naive women and a significantly higher proportion of vertebral fractures in aromatase inhibitor–treated women. The gene discussed is CYP19A1; the disease is breast carcinoma.