The epidemiology of primary hyperparathyroidism (PHPT) has generally been studied in Caucasian populations. The aim was to examine the incidence and prevalence of PHPT within a racially mixed population. A descriptive epidemiologic study was performed. The study population included 3.5 million enrollees within Kaiser Permanente Southern California. All patients with at least one elevated serum calcium level (>10.5 mg/dL, 2.6 mmol/L) between 1995 and 2010 were included. Cases of PHPT were identified by electronic query of laboratory values using biochemical criteria, after exclusion of secondary or renal and tertiary hyperparathyroidism cases. The incidence and prevalence rates of PHPT were calculated according to sex, race, age group by decade, and year. Initial case finding identified 15,234 patients with chronic hypercalcemia, 13,327 (87%) of which had PHPT as defined by elevated or inappropriately normal parathyroid hormone levels. The incidence of PHPT fluctuated from 34 to 120 per 100,000 person-years (mean 66) among women, and from 13 to 36 (mean 25) among men. With advancing age, incidence increased and sex differences became pronounced (incidence 12-24 per 100,000 for both sexes younger than 50 y; 80 and 36 per 100,000 for women and men aged 50-59 y, respectively; and 196 and 95 for women and men aged 70-79 y, respectively). The incidence of PHPT was highest among blacks (92 women; 46 men, P < .0001), followed by whites (81 women; 29 men), with rates for Asians (52 women, 28 men), Hispanics (49 women, 17 men), and other races (25 women, 6 men) being lower than that for whites (P < .0001). The prevalence of PHPT tripled during the study period, increasing from 76 to 233 per 100,000 women and from 30 to 85 per 100 000 men. Racial differences in prevalence mirrored those found in incidence. PHPT is the predominant cause of hypercalcemia and is increasingly prevalent. Substantial differences are found in the incidence and prevalence of PHPT between races.