Abstract: The deficiency disease of 5αreductase 2 is a common genetic disease of AR,which karyotype is 46,XY.As the boy patients were born,some abnormity in various degrees would occur on the majority of their external genitalia.Blurring of external genitalia or being similar to female phenotype is the most common phenomenon.Also,being close to normal external genitalia of male phenotype could be found.Some patients would visit a doctor on account of diminutive penis or maldevelopment of gonad.The boy patients who have the deficiency disease of 5αreductase 2 with diminutive penis would be inclined to be misdiagnosed or never diagnosed.Thus,the time for treatment would always be delayed.The article is a summary of genotype characteristics、pathogenesis、clinical feature、diagnostic basis and progress of treatment in allusion to the deficiency disease of 5αreductase 2 with diminutive penis.

Key words: micropenis, 5αreductase 2；diagnosis；treatment