From 1960 to 1990, one hundred twenty eight (128) subjects with primary hyperparathyroidism were operated in the University Hospital. The medical records were reviewed. Serum and urine chemistries were done by conventional methods, serum PTH was done by RIA's (N-, C-, and midregion) and intact by IRMA and 1,25 dihydroxycholecalciferol by a non equilibrium receptor assay from calf thymus and preceded by double Sep-Pak chromatography. The distal third of the radius (nondominant arm) was used to evaluate radial bone density (RBD), using single photon absorptiometry (Norland) and the lumbar bone density (LBD) was measured by dual energy X Ray absorptiometry (DEXA). The RBD was done in 41 females and 15 males and the LBD in 12 females and 4 males. The series comprised 95 females, age range from 15 to 79 years, and 33 males, age range from 14 to 69 years. Prominent clinical features included nephrolithiasis in 72 subjects (56%), osteitis fibrosa cystica in 2, isolated familial hyperparathyroidism in 4 subjects in one family, 7 subjects with MEN-1 in 3 families, and 4 subjects with MEN-2 in one family. Only 7 subjects were asymptomatic. Serum calcium was elevated in all, serum alkaline phosphatase was elevated in 24% and urinary hydroxiproline was increased in 48%. Serum phosphorus was low in 92%. PTH assay was either elevated or inappropriately normal for the serum calcium in all patients tested. Serum 1,25 D was elevated in 57%. The PTH level was positively correlated with the serum calcium (r = 0.70), but had no significant correlation with the serum phosphorus and the 1,25 D. The RBD expressed as the standard deviation from that of the mean for age and sex matched controls was > or = 2 SD below the mean in 39% of females and in 40% of males. In contrast to the RBD none of the subjects tested had a LBD > or = 2 SD below the age and sex adjusted mean. 103 subjects had adenomas, 20 primary hyperplasia, 2 carcinomas and in 3 surgical exploration was unsuccessful. As to the outcome of Surgery, 117 (93%) were cured. Thus, in this series, successful surgery for primary hyperparathyroidism is the rule. Primary hyperparathroidism is rarely asymptomatic and appendicular bone disease and nephrolithiasis are commonly seen.