How do anti-Müllerian hormone (AMH) concentrations in women with and without arthritis compare? Is there an association between AMH and arthritis drug regimen?In this prospective cohort study, AMH was measured at two time points (T0 and T1) in 129 premenopausal women with arthritis. AMH at T0 was compared with that from a bank of serum samples from 198 premenopausal women without arthritis. Primary outcomes were: (i) diminished ovarian reserve (DOR) (AMH <1.1 ng/ml) and (ii) annual rate of AMH decrease. Univariate, multivariable and Firth logistic regression identified variables associated with annual AMH decrease in excess of the 75th percentile.Median time between T0 and T1 was 1.72 years. At time T0, median age-adjusted AMH in women with arthritis was significantly lower than that of women without arthritis (median 2.21 ng/ml versus 2.78 ng/ml; P = 0.009). Women with arthritis at highest risk for DOR had a history of tubal sterilization or were over the age of 35. Those with highest odds of having an annual AMH decrease in excess of the 75th percentile (over 28% decrease per year) were those: over the age of 35 or who sought care for infertility. Women with arthritis taking methotrexate alone (OR 0.08, 95% CI 0.01–0.67) or methotrexate plus tumour necrosis factor-alpha antagonists (OR 0.13, 95% CI 0.02–0.89) were less likely to be in the highest quartile of annual AMH decrease than women with arthritis not taking medication.Women with arthritis had lower AMH than healthy controls. Long-term methotrexate use was not associated with an annual AMH decrease.