Good evidence from prospective and cross-sectional studies suggests that the overall prevalence of polycystic ovary syndrome (PCOS) is about 6%, but the prevalence is much higher in women of South Asian origin, who have more severe symptoms and present at a much younger age.

• In a cross-sectional study of 224 female volunteers (18–25 years of age) who had polycystic ovaries identified on ultrasonography, the prevalence of PCOS was as low as 8% or as high as 26%, depending on the diagnostic criteria used [Michelmore et al, 1999].
• A prospective study of 400 premenopausal women attending a pre-employment medical examination in the US found that the prevalence of PCOS (defined as oligo-ovulation, hyperandrogenaemia, or hirsutism, with the exclusion of related disorders) was 6.6% [Azziz et al, 2004].
• A prospective study of 277 women (129 white, 148 black) of reproductive age attending a pre-employment medical examination in the US found that the prevalence of PCOS (defined as oligo-ovulation, hyperandrogenaemia, or hirsutism, with the exclusion of related disorders) was 4% [Knochenhauer et al, 1998].
• A cross-sectional study of 192 women of reproductive age living on the Greek island of Lesbos found that the prevalence of PCOS (defined as oligomenorrhoea and biochemical hyperandrogenism) was 6.77% [Diamanti-Kandarakis et al, 1999].
• A prospective study of 154 white women in Spain of reproductive age attending spontaneously for blood donation found that the prevalence of PCOS (defined as oligomenorrhoea, or clinical or biochemical hyperandrogenism, with the exclusion of related disorders) was 6.5% [Asuncion et al, 2000].
• A study of 212 women 18–40 years of age from the Indian subcontinent, selected from GPs' lists in the UK, found a prevalence of polycystic ovaries of 52%. Menstrual disturbance was reported by 49% of those with polycystic ovaries and 16% of those without polycystic ovaries [Rodin et al, 1998].
• A case-controlled, cross-sectional study was carried out on 47 South Asian and 40 white European women with anovular PCOS who were seeking treatment for infertility. There was a small control group of age- and weight-matched women without PCOS (11 South Asian women, 22 white European women) [Wijeyaratne et al, 2002].
• The study found that the South Asian women:
• Sought treatment at a younger age (p = 0.005).
• Developed hirsutism significantly earlier (p = 0.01).
• Developed oligomenorrhoea earlier (p = 0.0001).
• Had a higher prevalence of secondary infertility (p = 0.03).
• Had higher fasting insulin concentrations (p = 0.0001).
• Affected women from both racial groups were significantly more hirsute than their corresponding control groups.
• Acanthosis nigricans was present in 55% of South Asian women and in 7% of white women but in none of the control groups.
• Acne was present in 66% of South Asian women and 30% of white women.