There are no epidemiologic studies documenting the prevalence of hyperparathyroidism in the US hemodialysis population. We looked at a random sample of 612 hemodialysis patients enrolled in 10 outpatient dialysis units in Mississippi. Fifty percent of the patients surveyed had an intact serum parathyroid hormone (PTH) level more than three times normal (mean, 622 pg/mL). Another 25% had a less than normal PTH level (mean, 33 pg/mL), suggesting adynamic bone disease. Abnormal serum calcium was also common. Seventeen percent of patients were hypocalcemic and 14% were hypercalcemic. These high point prevalences occurred despite widespread use of calcium supplements and/or vitamin D (used in 90% of the patients surveyed). Black patients tended to have a lower serum calcium and higher PTH level than white patients. We also found that diabetic patients are less likely to have an elevated PTH level than nondiabetic patients. Elevated serum phosphorus was the most important factor correlating with the development of secondary hyperparathyroidism. Causes of inadequate control of hyperparathyroidism in this population require further study.