The term, disorders of sexual differentiation, broadly represents a disjunction between genotype and phenotype. Phenotype in turn can refer to external or internal genital development. Disorders of sexual differentiation are determined at conception insofar as (1) the abnormal genotype is the aberrant genetic product of fertilization at the chromosomal level or (2) the abnormal phenotype results from postfertilization errors in function at the gene level, somewhere along the pathway of transcription and translation. In either event, the error is genetic, whether or not sporadic or inherited, even if the pathways have yet to be fully elucidated for a given disorder.