Since 1966, when it first appeared, and through nine editions, McKusick"s catalogue has been the definitive reference work on human genetic traits and disorders. Now in two volumes, the tenth edition contains a total of 5,710 entries, 869 more than the ninth, and presents information obtained through March 1, 1992. New in this edition are a guide to the use of OMIM and the genetic code in two alternative easy-to-use formats.