The influence of gender, age, body size, cholelithiasis, and obesity on fasting gallbladder volume (GBV) was investigated by real-time ultrasonography in a general population cohort of subjects whose ages were between 30 and 69 yr, living in Bari, a Southeastern Italian city. Of the 2076 subjects analyzed, 1246 (60%) were males and 830 (40%) were females (mean age 50 yr). Among them, 1703 subjects were healthy, 108 had gallstones, and 265 were obese. Fasting GBV in healthy individuals was larger in males (M) than in females (F) [M, 18.7 +/- 0.3 (SEM) ml vs. F, 17.0 +/- 0.3 ml; p less than 0.001] and obese (M, 23.4 +/- 1.5 ml vs. 19.7 +/- 0.9 ml; p less than 0.05). The trend was similar in gallstone patients, but it was not statistically significant (M, 23.0 +/- 2.0 ml vs. F, 18.8 +/- 1.5 ml; t = 1.64). Gallbladder size correlated positively with body size in the lean healthy population (p less than 0.01), increased with age in healthy nonobese males (p less than 0.01), and was smaller in healthy males than in males with gallstones (0.01 less than p less than 0.02) and obese, in both sexes (p less than 0.01). We conclude that fasting GBV 1) is larger in lean healthy and obese males than females, 2) increases with age in lean males and with body size in healthy lean females, and 3) is greater in patients with gallstones and in obese subjects, and this might partially account for the defective gallbladder motor function reported in these patients.