Hypoparathyroidism is a rare endocrine disorder whose incidence and prevalence have not been well defined. This study aimed to 1) estimate the number of insured adult patients with hypoparathyroidism in the United States and 2) obtain physician assessment of disease severity and chronicity. Prevalence was estimated through calculation of diagnoses of hypoparathyroidism in a large proprietary health plan claims database over a 12-month period from October 2007 through September 2008 and projected to the US insured population. Incidence was also calculated from the same database by determining the proportion of total neck surgeries resulting in either transient (≤6 months) or chronic (>6 months) hypoparathyroidism. A physician primary market research study was conducted to assess disease severity and determine the percentage of new nonsurgical patients with hypoparathyroidism. Incidence data were entered into an epidemiologic model to derive an estimate of prevalence. The diagnosis-based prevalence approach estimated 58,793 insured patients with chronic hypoparathyroidism in the United States. The surgical-based incidence approach yielded 117,342 relevant surgeries resulting in 8901 cases over 12 months. Overall, 7.6% of surgeries resulted in hypoparathyroidism (75% transient, 25% chronic). The prevalence of chronic hypoparathyroidism among insured patients included in the surgical database was estimated to be 58,625. The physician survey found that 75% of cases treated over the past 12 months were reported due to surgery and, among all thyroidectomies and parathyroidectomies and neck dissections performed in a year, 26% resulted in transient hypoparathyroidism and 5% progressed to a chronic state. In conclusion, the two claims-based methods yielded similar estimates of the number of insured patients with chronic hypoparathyroidism in the United States (∼58,700). The physician survey was consistent with those calculations and confirmed the burden imposed by hypoparathyroidism. © 2013 American Society for Bone and Mineral Research.