Excess parathyroid hormone (PTH) has long been considered detrimental to the health of patients with end-stage renal disease. PTH has been implicated as a multisystem uremic toxin, and hyperparathyroidism can be a debilitating complication in dialyzed patients. We have studied prospectively the relationship of enrollment serum intact PTH and various demographic characteristics and other biochemical parameters to all-cause mortality in 345 hemodialysis (HD) and 277 peritoneal dialysis (PD) patients. We monitored the patients for 14 years. Observed survival and survival after adjustment for age, race, gender, months on dialysis at enrollment, diabetic status, and nutritional markers were significantly better for patients with enrollment PTH greater than 200 pg/mL than for patients with PTH 65 to 199 pg/mL and patients with PTH less than 65 pg/mL. Enrollment serum PTH was an independent predictor of survival in HD and PD patients. For HD patients, age and months on HD at enrollment were associated inversely with PTH level, whereas black race, creatinine, and phosphorus were associated directly with PTH. For PD patients, age, diabetes, and months on PD at enrollment were inverse predictors, whereas black race, albumin, creatinine, and phosphorus were associated positively with PTH. Lower than expected levels of PTH in uremic patients is associated with increased mortality. We hypothesize that inadequate protein intake or phosphorus intake or both result in impaired development of the expected secondary hyperparathyroidism and in the excess mortality risk inherent with malnutrition.