Cryptorchidism, the most common congenital abnormality in newborn boys, is a major risk factor for male infertility and testicular malignancy in adulthood. This disorder appears as an isolated form or as part of impaired male sex development or a congenital malformation syndrome. Based mainly on the laboratory studies of the rodent models, sex steroidal signaling pathways have been shown to be involved in testicular descent; however, data on the human genetic susceptibility are less compelling. Mutations in the human genes encoding androgen receptor (AR), estrogen receptor alpha (ERalpha) and beta (ERbeta), and steroidogenic factor-1 (SF-1) have occasionally been identified but do not seem to be a frequent cause of this genital malformation. On the other hand, common polymorphisms in these genes have recently been investigated as possible contributing risk factors for idiopathic isolated (nonsyndromic) cryptorchidism, alone or by influencing susceptibility to other causal factors such as environmental endocrine disruptors. Abbreviations: Androgen Receptor (AR); DNA-Binding Domain (DBD) ;Environmental Estrogen Disruptors (EEDs); Estrogen Receptor Alpha (ERalpha); Estrogen Receptor Beta (ERbeta); Ligand-Binding Domain (LBD); Linkage Disequilibrium (LD); Odds Ratio (OR); Restriction Fragment Length Polymorphism (RFLP); Single Nucleotide Polymorphism (SNP); Steroidogenic Factor-1 (SF-1); Transactivation Domain (TAD); Testicular Dysgenesis Syndrome (TDS); Wild Type (WT).