The clinical presentations of 17β hydroxysteroid dehydrogenase type 3 (17β-HSD3) deficiency, 5α-reductase type 2 deficiency, and complete androgen insensitivity syndrome can be similar. However, those with 17β-HSD3 deficiency and 5α-reductase type 2 deficiency will develop virilization and should undergo gonadectomy after genetic testing before the age of puberty if reared in the female sex. Two sisters were initially diagnosed with complete androgen insensitivity syndrome as young children after testes were discovered during hernia surgery. Virilization occurred in both sisters during puberty, and a diagnosis of 17β-HSD3 deficiency was suspected. Confirmatory diagnosis through gene sequencing identified a heterozygous mutation for both a known splicing mutation and a previously unreported amplification mutation of the HSD17B3 gene.