OBJECTIVE: To examine whether accounting for a woman's age and body mass index (BMI) would improve the ability of antimüllerian hormone (AMH) to distinguish between women with (cases) and without (controls) polycystic ovarian syndrome (PCOS). DESIGN: An opportunistic case-control dataset of reproductive age women having evaluations for PCOS as defined by National Institutes of Health criteria. SETTING: Two medical centers in the United States enrolled women. Serum samples were analyzed for relevant analytes. PATIENTS: Women were between 18 and 39 years of age when samples and clinical information were collected. Residual samples had been stored for 2-17 years. AMH was measured via immunoassay. INTERVENTIONS: None; this was an observational study. MAIN OUTCOME MEASURES: Detection and false-positive rates for PCOS were computed for AMH results expressed as multiples of the median (MoM) both before and after adjustment for the woman's age and BMI. RESULTS: Using unadjusted AMH MoM results, 168 cases (78%) cases were at or beyond the 90(th) centile of controls (2.47 MoM). After accounting for each woman's age and BMI, 188 (87%) of those women were beyond the 90(th) centile of controls (2.20 MoM), a significant increase (P = .015). The adjusted AMH MoM levels fitted logarithmic normal distributions well (mean, standard deviation for controls and cases of 0.0000, 0.2765 and 0.6884, 0.2874, respectively) and this allowed for computation of patient-specific PCOS risks. CONCLUSIONS: Accounting for the woman's age and BMI resulted in significantly higher AMH-based detection rates for PCOS at a 10% false-positive rate, and patient-specific PCOS risks could be computed.