It remains controversial whether anti-Müllerian hormone (AMH) concentration is influenced by hormonal contraception. This study quantified the effect of hormonal contraception on both endocrine and sonographic ovarian reserve markers in 228 users and 504 non-users of hormonal contraception. On day 2-5 of the menstrual cycle or during withdrawal bleeding, blood sampling and transvaginal sonography was performed. After adjusting for age, ovarian reserve parameters were lower among users than among non-users of hormonal contraception: serum AMH concentration by 29.8% (95% CI 19.9 to 38.5%), antral follicle count (AFC) by 30.4% (95% CI 23.6 to 36.7%) and ovarian volume by 42.2% (95% CI 37.8 to 46.3%). AFC in all follicle size categories (small, 2-4mm; intermediate, 5-7mm; large, 8-10mm) was lower in users than in non-users of hormonal contraception. A negatively linear association was observed between duration of hormonal-contraception use and ovarian reserve parameters. No dose-response relation was found between the dose of ethinyloestradiol and AMH or AFC. This study indicates that ovarian reserve markers are lower in women using sex steroids for contraception. Thus, AMH concentration and AFC may not retain their accuracy as predictors of ovarian reserve in women using hormonal contraception. Serum anti-Müllerian hormone (AMH) concentration is an indirect marker of the number of small follicles in the ovary and thereby the ovarian reserve. The AMH concentration is now widely used as one of the markers of the ovarian reserve in ovarian hormonal stimulation regimens. Hence the AMH concentration in a patient is used to decide the dose of the ovarian hormonal stimulation prior to IVF treatment. In some infertile patients, hormonal contraception is used prior to ovarian hormonal stimulation and therefore it is important to clarify whether serum AMH concentration is influenced by the use of sex steroids. The aim of this study was to quantify the potential effect of hormonal contraception on the ovarian function by hormonal analyses and ovarian ultrasound examination. Examinations were performed in the early phase of the menstrual cycle or the hormone-free interval of hormonal contraception. We compared the AMH concentration, the antral follicle count (AFC) and the ovarian volume in 228 users versus 504 non-users of hormonal contraception. Users of hormonal contraception had 29.8% lower AMH concentration, 30.4% lower AFC and 42.2% lower ovarian volume than non-users. These findings were more pronounced with increasing duration of hormonal contraception. No dose-response relation was found between the dose of ethinylestradiol and the impact on serum AMH and AFC. The study indicates that ovarian reserve markers are lower in women using sex steroids for contraception. Thus, serum AMH concentration and AFC may not retain their accuracy as predictors of the ovarian reserve in women using hormonal contraception.