Abstract Study question Does serum Kisspeptin (KP) levels discriminate between fertile and infertile women with polycystic ovary syndrome (PCOS)? Summary answer Serum KP levels can be used as a potential discriminatory biomarker for infertility in women with PCOS. What is known already PCOS is the most common cause of anovulatory infertility and not fully elucidated pathology. A persistent rapid gonadotropin-releasing hormone (GnRH) pulse frequency in patients with PCOS exist throughout ovulatory cycle. KP is a neuropeptide that increases GnRH pulsatile release during ovulation. Therefore, KP may have a key role as a central regulator of fertility in PCOS patients. Although, recent studies showed that the KP concentration is higher in PCOS patients, the evidence is limited as to whether serum KP levels determine infertility in PCOS. Study design, size, duration This was a single center prospective cohort study conducted at Goztepe Prof. Dr. Suleyman Yalcin City Hospital Affiliated to Istanbul Medeniyet University, Istanbul, Turkey between January 2023 to February 2023. Our study enrolled 30 fertile and 30 infertile women with PCOS, who were aged between 18 and 45 years. PCOS was defined according to the criteria of the Rotterdam ESHRE- ASRM sponsored consensus group (2004). Participants/materials, setting, methods Venous blood samples from the participants were obtained after fasting and between 8 a.m. and 10 a.m. on days 2-5 of the menstrual cycle. Samples were thawed, and a human KISS1 (Kisspeptin 1) ELISA kit (Elabscience, USA,lot no:E-EL-H5618) was applied to measure KP serum concentrations. Patient characteristics and KP concentrations were compared among the two groups. Statistical analysis was performed by Mann-Whitney, Spearman correlations, and linear regression analysis. A p-value <0.05 was considered significant. Main results and the role of chance The mean age of the patients was 27.57±5.39 years in the fertile PCOS group and 26.80± 4.85 years in the infertile PCOS group (p = 0.63). There was no significant difference among the groups in terms of body mass index (BMI), duration of infertility, serum FSH, LH, LH-to-FSH ratio, E2, antimullerian hormone (AMH), TSH, prolactin, 17OHP, total testosterone, SHBG, HbA1c, HOMA-IR, neutrophil–lymphocyte ratio levels and antral follicle count (AFC). DHEA-S was significantly higher in the infertile PCOS group (306.73±94.869 mcg/ dL), compared to the fertile PCOS group (258.08±84.29 mcg/ dL, p = 0.037). The mean KP level was significantly higher in the infertile PCOS group (444.80±136.61 ng/ mL), compared to the fertile PCOS group (333.02±131.10 ng/ mL, p = 0.001). The KP level was positively correlated with AFC, AMH, and total testosterone levels (R = 0.495, R = 0.548, R = 0.362, p < 0.05, respectively) in the infertile PCOS group. Furthermore, ROC analysis showed that the optimal cut-point value was found to be 285.59. When this cut-off value of serum KP levels was taken, the sensitivity was 0.96 and the specificity was 0.50. Linear regression analysis revealed that AMH was positively associated with KP levels (p = 0.022). Limitations, reasons for caution Due to the limited number of women with available samples, we were not able to analyze KP serum levels according to specific PCOS phenotypes Wider implications of the findings Serum KP levels are higher in infertile women with PCOS compared to fertile women with PCOS. Infertility caused by PCOS can be predicted by serum KP levels. In the future identification, KP in PCOS may be applied to develop potential therapeutic agents. Trial registration number Not applicable