Tamoxifen is an antiestrogenic drug which is used in the treatment of breast cancer and nonmalignant breast disorders. It also has a stimulating effect on the secretion of hypofisar gonadotropic hormones and is generally used in the treatment of infertility. In males, tamoxifen causes an increase of endogenous production of androgenic steroids, and therefore is used by athletes. A method for identification of tamoxifen and metabolites in urine, using the gas chromatography and mass spectrometry system (GC/MS) is described. This study also reports the extraction methodology of tamoxifen and metabolites in urine samples of healthy male volunteers and the GC/MS conditions used to identify tamoxifen and its metabolites.