This study was undertaken to evaluate the relation between hip fractures and nocturnal micturition habits in elderly men and women. A questionnaire survey was undertaken among 10,216 elderly subjects. The mean (+/-S.D.) ages of the men and women were 73.0+/-6.0 and 72.6+/-6.7 years, respectively. A hip fracture during the past five years had occurred in 97 (3.9%) of the men and 175 (4.6%) of the women and the occurrence increased with increasing age in both sexes. In both men and women nocturnal micturition increased with age. Among men, passing of subjectively large amounts of urine at night was reported to occur never or very seldom in 63.3% and rather seldom, rather often, and very often in 21.9%, 12.7%, and 2.1%, respectively. The corresponding frequencies in women were 65.1%, 17.2%, 13.7%, and 3.9%, respectively. Multiple logistic regression analysis with sex, nocturia, and nocturnal voided volumes as independent variables and occurrence of hip fracture during the last five years as the dependent variable showed that the risk of having had a hip fracture was increased by nocturia three or more episodes versus two or fewer; odds ratio (OR) 1.8, confidence interval (CI) 1.1-3.0, and by large nocturnal urine volumes, very often versus very seldom or never; (OR 3.5; CI 1.8-7.3). One can conclude that in these elderly subjects the risk of hip fractures during a five-year period was increased independently by increased nocturnal micturition and increased nocturnal urine output.