Androgen excess is a key feature of the polycystic ovary syndrome; however the molecular mechanisms underlying its pathogenesis largely remain elusive. Dehydroepiandrosterone sulfate (DHEAS) is the most abundant steroid in the human circulation but only unconjugated dehydroepiandrosterone (DHEA) can be converted to active androgens. Conversely, conversion of DHEA to its sulfate ester DHEAS by DHEA sulfotransferase, SULT2A1, diminishes the DHEA pool available for androgen generation. SULT2A1 requires 3′-phosphoadenosine-5′-phosphosulfate (PAPS), a product of the two human isoforms of PAPS synthase, PAPSS1 and PAPSS2, for catalytic activity. Here, we investigated a girl of Turkish origin who presented with premature pubarche at 6 years, progressing to polycystic ovary syndrome with hirsutism, acne, and secondary amenorrhoea at 13 years. Circulating androgen precursors (DHEA, androstenedione) and active androgens (testosterone, dihydrotestosterone) were elevated. By contrast, serum DHEAS was below the limit of detection (0.40 μmol/l), suggestive of impaired DHEA sulfation. Sequencing of index case and parental DNA revealed no SULT2A1 or PAPSS1 mutations, but demonstrated compound heterozygous PAPSS2 mutations in the affected girl, T48R and R329X, and parental heterozygosity. Neither mutation was recorded upon sequencing of a healthy control cohort (n=100), excluding that T48R and R329X represent polymorphisms. In vitro reconstitution of the DHEA sulfation system utilising bacterially expressed human SULT2A1 and wild-type and mutant PAPSS2 confirmed the disease-causing nature of the mutants (T48R 6.0±0.6% of wild-type activity; R329X 0%). In silico analysis demonstrated that T48R is a highly conserved residue located within the p loop of the PAPSS2 APS kinase domain, an area crucial for function, whereas R329X results in early truncation of the ATP sulfurylase domain of PAPSS2. These findings indicate a crucial role for DHEA sulfation as a gate keeper of human androgen synthesis and question the use of high androstenedione and high DHEAS levels to define ovarian versus adrenal hyperandrogenism.