Betatrophin is defined as a new marker in glucose homeostasis and lipid metabolism. We aimed to investigate the role of serum betatrophin in full-blown polycystic ovary syndrome (PCOS) patients and 47-aged healthy women, 51 full-blown PCOS patients were included in this cross-sectional study. Betatrophin concentrations were significantly lower in PCOS group and displayed a positive correlation only with serum tryglyceride in control group (p < .05). A cutoff level (464.5 ng/L) was determined for betatrophin according to Receiver Operating Characteristic curve. Using this value, 64.7% of PCOS patients were classified as below the cutoff and in this group betatrophin was found to correlate negatively with fasting glucose, fasting insulin, and homeostasis model assessment of insulin resistance (p = .038, p = .020, and p = .014, respectively), and positively with total testosterone (p = .041). In the rest of PCOS cases (35.3%) who had betatrophin higher than cutoff, positive correlation was found with low-density lipoprotein cholesterol (p = .009). In conclusion, betatrophin levels are reduced in full-blown PCOS patients who had worse metabolic phenotype.