Nonclassical 3β-hydroxysteroid dehydrogenase deficiency (NC3β-HSD) is a common autosomal recessive disorder of adrenal steroidogenesis that may occur more frequently than nonclassical 21-hydroxylase deficiency. Early appearance of pubic hair and/or axillary hair are common but not specific for the diagnosis of NC3β-HSD in children. Adult women usually present with signs of androgen excess such as hirsutism, acne, temporal balding, irregular menses, and infertility. Among 759 women with signs of androgen excess reviewed in the literature, the prevalence for NC3β-HSD was 15.9%. The diagnosis of NC3β-HSD relies upon elevated Δ5over Δ4-steroid ratios either after an ACTH stimulation test or using urinary 24-hr hormonal concentrations. Baseline serum hormonal concentration measurements are insufficient for the diagnosis. Diagnostic ACTH testing should be carried out in children and women with signs of androgen excess because, if present, the disorder has a specific therapy in low-dose glucocorticoid administration.