Disorders of sex development (DSDs) are a genetically and clinically heterogeneous group of congenital conditions of the urogenital tract and reproductive system. Time and spatially controlled transcription factors, signal molecules, and an array of different hormones are involved in the development of sex characteristics, and variations in their pathways and actions are associated with DSD. These conditions may be caused by numerical or structural variations in sex chromosomes as well as autosomes, variations in genes involved in gonadal and/or genital development, and changes in gonadal and/or adrenal steroidogenesis. Endogenous or exogenous (maternal) and possibly endocrine disruptors may also interfere with genital development.