OBJECTIVE: Polycystic ovary syndrome (PCOS) is the leading cause of infertility in women of reproductive age. Its diagnosis can be challenging due to the heterogeneity of presentation, the lack of a single definitive test, and the need to rule out other conditions. The diagnostic criteria are difficult to apply consistently across different individuals and ethnic groups. The study aimed to define a threshold of anti-Müllerian hormone (AMH), which would be predictive of PCOS in the Tunisian population. METHODS: A case-control study was conducted, including 31 women diagnosed with PCOS according to the Rotterdam criteria, and 31 age- and body mass index-matched women without PCOS. All participants underwent medical evaluations, including gynecologic history, physical examination, ovarian ultrasound, and measurements of serum AMH and testosterone concentrations. RESULTS: Serum AMH concentrations were noticeably higher in women with than those without PCOS [median (25th-75th percentile), 6.92 (4.60-10.0) ng/mL versus 1.90 (1.33-2.85) ng/mL; P < 0.001]. A serum AMH concentration of 3.41 ng/mL differentiated women with PCOS from control women with excellent accuracy (median area under the curve, 0.977; sensitivity, 97%; and specificity, 90%). AMH levels were positively correlated with the number of antral follicles (Spearman's r = 0.846; P < 0.001), ovarian volume (Spearman's r = 0.769; P < 0.001), and testosterone levels (Spearman's r = 0.654; P < 0.001). PCOS phenotype A was associated with the highest AMH levels. CONCLUSION: The study suggests that serum AMH is relevant for the diagnosis of PCOS. Based on the findings, we propose a serum AMH cutoff value of 3.41 ng/mL for the diagnosis of PCOS in Tunisian hyperandrogenic adult women.