More than twenty heterocyclic aromatic amines (HAAs) have been identified in grilled meats, fish, poultry, and tobacco smoke condensate. HAAs are carcinogens and induce tumors at multiple sites in experimental laboratory animals. Because of the widespread occurrence of HAAs in foods, these chemicals may contribute to the etiology of several common human cancers that are associated with frequent consumption of grilled meats including colon, rectum, prostate, and breast. HAAs require metabolism in order to exert their genotoxic effects. Metabolic activation occurs by N-hydroxylation, a reaction catalyzed by cytochromes p450 (CYP). Some N-hydroxy-HAA metabolites may directly react with DNA, but further metabolism by N-acetyltransferases (NATs) or sulfotransferases (SULTs) may occur to form highly reactive N-acetoxy or N-sulfonyloxy esters that readily react with DNA bases. The N-acetoxy ester of the HAA 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) is detoxified by glutathione S-transferases (GSTs), which catalyze the reduction of the reactive intermediate back to the parent amine. Some HAAs also undergo detoxification through conjugation reactions with the phase II enzymes such as UDP-glucuronosyltransferases (UGTs) or SULTs to form stable, polar products that are readily eliminated. All of these xenobiotic metabolism enzyme systems (XMEs) display common genetic polymorphisms, which may affect protein expression, protein stability, catalytic activity, and thus, the biological potency of these procarcinogens. In this review, the roles of common genetic polymorphisms of XMEs involved in HAA metabolism and cancer risk are discussed.