Polycystic ovary syndrome (PCOS) is one of the most common endocrinopathies in reproductive age women and insulin resistance (IR) and hyperinsulinism play a critical role in the pathogenesis. Glucagon-like peptide-1 (GLP-1), promotes insulin secretion, inhibits glucagon secretion. GLP-1 is degraded by dipeptidyl peptidase-4 (DPP-4). DPP-4, also interacts with adenosine deaminase (ADA). Therefore, IR may have a significant connection with ADA activity. The aim of this study is to compare levels of DPP-4 and ADA enzymes in PCOS and infertile patients. Forty-four patients with PCOS and 44 infertile patients with normal ovarian reserve were enrolled in the study. Serum ADA, DPP-4, AMH, glucose and insulin levels were measured. HOMA-IR method was used to assess insulin sensitivity. ADA, DPP-4, AMH, HOMA-IR (p < .05) and insulin levels (p < .01) were found to be increased in PCOS patients. Considering all study participants AMH levels were found to be positively correlated with ADA (r: 0.734) and DPP-4 (r: 0.449) levels. Also ADA levels were found to be positively correlated with DPP-4 (r: 0.472), insulin (r: 0.216) and HOMA-IR (r: 0.223). Our findings about the elevation of DPP-4 levels in patients with PCOS suggest that the use of DPP-4 inhibitors may be beneficial in treatment of these patients.