Abstract
Approaches to the study of the genetic basis of common complex diseases and their clinical applications are considered. Monogenic Mendelian inheritance in such conditions is infrequent but its elucidation may help to detect pathogenic mechanisms in the more common variety of complex diseases. Involvement by multiple genes in complex diseases usually occurs but the isolation and identification of specific genes so far has been exceptional. The role of common polymorphisms as indicators of disease risk in various studies is discussed.