difficult to distinguish from other causes of 46,XY DSD (e.g., partial androgen insensitivity syndrome and 17β- hydroxysteroid dehydrogenase type 3 enzyme deficiencies). The measurement of the serum DHT concentration is challenging since the concentrations are low and DHT has a high level of cross-reactivity. A high level of assay specificity is required to measure concentrations of DHT since serum T levels are generally 10 fold higher than DHT in young males. Endocrinological tests for T/DHT ratios can be difficult to interpret since the normal ratio level varies according to age and severity of 5αR2 activity impairment. Affected young males of at least pubertal age with normal serum T levels demonstrate elevated T/DHT levels (normal T, lower than normal DHT). Stimulation with human chorionic gonadotropin (hCG) (alternatively, testosterone enanthate) is required in prepubertal children (with stimulation and samples taken over several days) to increase serum testosterone levels for measurement. Interpreting T/DHT ratios in male newborns is especially challenging due to neonatal testosterone surge and higher than normal 5a-reductase type 1 activity. SRD5A2 gene analysis is recommended for diagnosis in newborns. Broadly, 5αR2D is diagnosed with T/DHT ratios greater than 18 while ratios greater than 30 have been observed in severely affected individuals. 5αR2D can also be indicated by low ratios of 5α- to 5ß- reduced steroids, as measured in urine measured via gas chromatography–mass spectrometry. Ultrasonography is the primary means for assessing internal reproductive organs for diagnosis while genitography and voiding cystourethrography are used to resolve structures such as urethral and vaginal tracts. The use of pelvic MRI for diagnostic imaging for 5αR2D remains controversial. Management One of the most clinically challenging and controversial topics with 46,XY DSD is the practice of "sex assignment" or "sex of rearing". This is especially so in 5αR2D, since most affected individuals have undervirilized genitalia at birth but virilize to varying degrees at puberty. Historically most 5αR2D individuals have been "raised as females", but later reports show that over half of patients who underwent virilizing puberty adopted a male gender identity thus challenging historical practices. The goal of sex assignment/of rearing is to facilitate the greatest likelihood of a concordant gender identity in the patient's adulthood. The factors that contribute to gender identity are complex and not easy to report but some factors that contribute include sex chromosomes, androgen exposure, psychosocial development, cultural expectations, family dynamics and social situation. Female sex of rearing in 5αR2D