In addition to the well-known uremia-related factors calcium, phosphate, and vitamin D, genetic polymorphisms and gene mutations appear to have a role as well in modulating parathyroid function. Allelic polymorphisms of the vitamin D receptor gene have been most often examined but to date their precise place is not yet certain in patients with chronic renal failure. The frequent transformation of parathyroid cell proliferation from polyclonal to monoclonal growth in patients with severe secondary hyperparathyroidism must be attributed to mutations or deletions of various tumor-suppressor genes, and probably more rarely also to an activation of tumor-enhancer genes. © 2001 by the National Kidney Foundation, Inc.