CYP2C9 and CYP2C19 are important drug metabolizing enzymes and together metabolize about 18% of currently available drugs. Some of the important groups of drugs that are metabolized by them are antihypertensives, hypoglycemics, anticonvulsants, antiulcer drugs etc. Genes encoding these enzymes are polymorphically expressed. Thirty variant alleles for CYP2C9 and 21 for CYP2C19 have been reported. The frequencies of these polymorphic alleles show marked inter-ethnic variation. Several reports have been published showing the clinical importance of this polymorphism. This review summarizes the currently available important information on this topic.