OBJECTIVE: Polycystic ovary syndrome (PCOS) is a common endocrine condition underpinned by insulin resistance and associated with increased risk of obesity, type 2 diabetes and adverse cardiovascular risk profile. Previous data suggest autonomic imbalance [elevated sympathetic nervous system (SNS) activity and decreased heart rate variability (HRV)] as well as endothelial dysfunction in PCOS. However, it is not clear whether these abnormalities are driven by obesity and metabolic disturbance or whether they are independently related to PCOS. PARTICIPANTS AND METHODS: We examined multiunit and single-unit muscle SNS activity (by microneurography), HRV (time and frequency domain analysis) and endothelial function [ischaemic reactive hyperaemia index (RHI) using the EndoPAT device] in 19 overweight/obese women with PCOS (BMI: 31.3 +/- 1.5 kg/m2 , age: 31.3 +/- 1.6 years) and compared them with 21 control overweight/obese women (BMI: 33.0 +/- 1.4 kg/m2 , age: 28.2 +/- 1.6 years) presenting a similar metabolic profile (fasting total, HDL and LDL cholesterol, glucose, triglycerides, insulin sensitivity and blood pressure). RESULTS: Women with PCOS had elevated multiunit muscle SNS activity (41 +/- 2 vs 33 +/- 3 bursts per 100 heartbeats, P <0.05). Single-unit analysis showed that vasoconstrictor neurons were characterized by elevated firing rate and probability and incidence of multiple spikes (P <0.01 for all parameters). Women with PCOS also had impaired endothelial function (RHI: 1.77 +/- 0.14 vs 2.18 +/- 0.14, P <0.05). HRV did not differ between the groups. CONCLUSION: Women with PCOS have increased sympathetic drive and impaired endothelial function independent of obesity and metabolic disturbances. Sympathetic activation and endothelial dysfunction may confer greater cardiovascular risk in women with PCOS.