To evaluate the risk factors for early osteoporosis in consecutive patients with fracture of the distal forearm, a population-based case-control study was carried out using postal questionnaires supplemented by interviews when necessary. All men and women between the ages of 40 and 80 years who were resident in the County of Uppsala (population 265,000) and who sustained a fracture of the distal forearm during a defined 12-month period were initially included. Of 427 cases, 385 (90.2%) replied. Those with previous fragility fractures were excluded, leaving 367 patients in the study (mean age 61.9 +/- 10.6 years): 302 women (mean age 62.8 +/- 10.1 years) and 65 men (mean age 57.5 +/- 11.8 years). For each patient an age- and sex-matched control without previous fragility fractures was selected from the population register. The questionnaire concerned heredity, diseases and medications, general health, tobacco smoking and physical activity. Reproductive variables and postmenopausal hormone replacement therapy were analyzed extensively. In neither sex were any significant, consistent differences found with regard to chronic diseases, medications, physical activity or smoking. In females heredity for fractures (odds ratio, OR = 1.46) was associated with an increased risk. Nulliparous women had an increased risk of forearm fractures (OR = 1.72) while late menopause (OR = 0.95) and postmenopausal oestrogen therapy > 2 years (OR = 0.44) appeared to be protective. It is concluded that lifestyle factors did not discriminate between fracture patients and controls in this strict population-based investigation, suggesting that in affluent Western societies, with their high fracture rate, most individuals have an osteoporosis-prone way of life.(ABSTRACT TRUNCATED AT 250 WORDS)