Objective: To evaluate a new fully automated assay measuring antimüllerian hormone (AMH; Roche Elecsys) against antral follicle count in women of reproductive age. Design: Prospective cohort study. Setting: Hospital infertility clinics and academic centers. Patient(s): Four hundred fifty-one women aged 18 to 44 years, with regular menstrual cycles. Intervention(s): None. Main Outcome Measure(s): AMH and antral follicle count (AFC) determined at a single visit on day 2-4 of the menstrual cycle. Result(s): There was a statistically significant variance in AFC but not in AMH between centers. Both AFC and AMH varied by age (overall Spearman rho -0.50 for AFC and -0.47 for AMH), but there was also significant between-center variation in the relationship between AFC and age but not for AMH. There was a strong positive correlation between AMH and AFC (overall spearman rho 0.68), which varied from 0.49 to 0.87 between centers. An agreement table using AFC cutoffs of 7 and 15 showed classification agreement in 63.2%, 56.9% and 74.5% of women for low, medium, and high groups, respectively. Conclusion(s): The novel fully automated Elecsys AMH assay shows good correlations with age and AFC in women of reproductive age, providing a reproducible measure of the growing follicle pool.