['To determine the prevalence of vertebral fractures in patients with mild asymptomatic primary hyperparathyroidism and to ascertain whether this prevalence is increased in comparison with the rate in a retrospective control group previously studied at the same institution or with current estimates of the risk for vertebral fractures in subjects of similar age.', 'Prospectively collected data were retrospectively analyzed and compared with data from a historical control group at the same institution and with published data.', 'The outpatient department of a bone and mineral metabolism clinic.', 'A consecutive series of patients with mild asymptomatic primary hyperparathyroidism diagnosed between 1 January 1976 and 31 December 1985. Criteria for inclusion in the study were the absence of symptoms due to hyperparathyroidism, no current kidney stone disease, no radiographic evidence of osteitis fibrosa, a serum calcium level of less than 3.00 mmol/L, a serum creatinine level of less than 133 mumol/L, and a forearm bone density value not more than 2.5 standard deviations below the age-, sex-, and race-adjusted normal value.', 'A conservative nonintervention study.', 'The prevalence of vertebral fractures in 174 patients (mean age, 62 years) with mild asymptomatic primary hyperparathyroidism was 1.7%; in a subset of white women, the prevalence was 2.8%. These rates were not higher than those expected, by comparison with the rate in a retrospective control group or with the risk for vertebral fractures in subjects of similar age, and may even be lower.'] Is mild asymptomatic primary hyperparathyroidism a risk factor for vertebral fractures?