Obesity has been associated with an increased risk of colonic diverticulosis. Evidence for this association is limited. We assessed whether anthropometric measures of obesity were associated with colonic diverticulosis.We analyzed data from a prospective study of 623 patients undergoing screening colonoscopies from 2013 through 2015; colonoscopies included examinations for diverticulosis. Body measurements were made the day of the procedure. Multivariate analyses were performed using modified Poisson regression to estimate prevalence ratios (PRs) and 95% CIs while adjusting for confounding variables. All analyses were stratified by sex.Among men, there was no association between any measure of obesity and diverticulosis. After adjustment, women with an obese body mass index (BMI ≥ 30) had an increased risk of any diverticulosis (PR, 1.48; 95% CI, 1.08-2.04) compared with women with a normal body mass index (BMI 18.5-24.9). The strength of this association was greater for more than 5 diverticula (PR, 2.05; 95% CI, 1.23-3.40). There was no significant association between measures of central obesity and diverticulosis in women. Stratified by sex, colonic diverticulosis was significantly less prevalent in women compared with men before the age of 51 years (29% vs 45%, P = .06). The prevalence of diverticulosis did not differ by sex in older age groups.In an analysis of data from 623 patients undergoing screening colonoscopies, we found that obesity (BMI ≥30) significantly increased the risk of colonic diverticulosis in women but not men. Colonic diverticulosis was less prevalent in premenopausal-age women compared with similar-age men. These findings suggest that sex hormones may influence the development of diverticulosis.