The impact of primary hyperparathyroidism (HPT) on the population has not been well documented, particularly with respect to asymptomatic HPT. Only 83 deaths were attributed to hyperparathyroidism in the United States in 1999, for a reported death rate of just 0.3 per million per year. Many more patients are affected, of course, and the national hospitalization rate for HPT was 8.0 per 100,000 in 1999, counting 22,000 "all-listed" diagnoses, and 1.8 per 100,000 counting only the 5000 admissions where HPT was the first-listed discharge diagnosis. Surgery was performed on approximately 12,000 hospitalized patients in the United States in 1999, for a parathyroidectomy rate of about 4.4 per 100,000 per year. Overall, the annual incidence of HPT was 20.8 per 100,000 in Rochester, MN, during 1983-1992, although this represented a substantial decline from incidence rates reported a decade earlier. There are no estimates of HPT prevalence from this country, but the figure was 4.3 per 1000 in one Swedish survey. By any of these measures, HPT is more common in women than men and increases with aging in both sexes. Other risk factors are obscure. The cost of parathyroidectomies for HPT has been estimated at $282 million annually in the United States, but no reliable estimate of overall expenditures for HPT has been made, and no formal assessment of the cost-effectiveness of any treatment approach has been carried out. Better data on the disability and costs related to HPT and its treatment will be needed to devise the most efficient approaches to patient management.