BACKGROUND Parathyroid cancer is a rare cause of hyperparathyroidism. The objectives of this study were to determine the patterns of disease, treatment trends, and outcomes among patients with parathyroid cancer by using a population-based data source. METHODS Surveillance, Epidemiology, and End Results (SEER) cancer registry data were used to identify patients who were diagnosed with parathyroid cancer from 1988 through 2003. To assess whether the incidence rate, treatment, tumor size, and cancer stage changed over time, the Cochrane-Armitage trend test was used, and Cox proportional-hazards modeling was used to identify the factors associated with an improved overall survival rate. RESULTS From 1988 through 2003, 224 patients with parathyroid cancer were reported in the SEER data. Over that 16-year study period, the incidence of parathyroid cancer increased by 60% (1988-1991, 3.58 per 10,000,000 population; 2000-2003, 5.73 per 10,000,000 population). Most patients (96%) underwent surgery (parathyroidectomy, 78.6% of patients; en bloc resection, 12.5% of patients; other, 4.9% of patients). The rate of surgical treatment increased significantly during the study period. The 10-year all-cause mortality rate was 33.2%, and the 10-year cancer-related mortality rate was 12.4%. Patient age (P<.0001), sex (P=.0106), the presence of distant metastases at diagnosis (P=.0004), and the year of diagnosis (P=.0287) were associated significantly with the overall survival rate. Tumor size, lymph node status, and type of surgery were not associated significantly with the overall survival rate. CONCLUSIONS Although parathyroid cancer is rare, the incidence increased significantly in the United States from 1988 through 2003. Young age, female gender, recent year of diagnosis, and absence of distant metastases were associated significantly with an improved survival rate.