Background Although lower bone mineral density (BMD) is considered to have an increased risk for colorectal adenoma, no association between marrow fat content and colorectal adenoma has been elucidated yet. Purpose To evaluate the relationship between marrow fat fraction (MFF) and the presence of colorectal adenoma in postmenopausal women using magnetic resonance spectroscopy (MRS). Material and Methods We performed a cross-sectional observational study on 152 postmenopausal patients with colorectal adenoma and 100 matched control subjects who underwent screening colonoscopy, biochemical measurements, dual-energy X-ray absorptiometry, and MRS. Logistic regression models were performed to assess the relationships among BMD, MFF, and colorectal adenoma. Results With univariate analysis, marrow fat accumulation was higher and BMD values were lower in patients with colorectal adenoma compared with those in controls. After adjustment for potential confounders including demographics, health history, blood lipid levels, indexes of glucose metabolism, and validated measures of diet and physical activity, MFF was significantly positively associated with colorectal adenoma (odds ratio [OR], 1.64; 95% confidence interval [CI], 1.10-2.46; P=0.008). Vertebral BMD, but not total hip and femoral neck BMD, was inversely related with colorectal adenoma (OR, 0.62; 95% CI, 0.14-0.89; P=0.027). Additionally, MFF was associated with adenoma number, size, and high-risk adenoma (all P<0.01). MFF was found to be an independent risk factor of a high-risk colorectal adenoma (OR, 2.08; 95% CI, 1.24-3.60; P=0.019). Conclusion Marrow fat accumulation is highly associated with colorectal adenoma, particularly high-risk adenoma, in postmenopausal women.