While multiple investigators have demonstrated that Müllerian inhibiting substance (MIS) concentration is an accurate marker of ovarian reserve, all previous reports have focused on patients aged 36 and younger. It remains to be seen if MIS concentration is a useful marker in patients with the highest prevalence of diminished ovarian reserve: those aged 37 and over. Day 2 MIS concentrations in patients aged 37 and over undergoing IVF were examined, and the predictive value of MIS concentration was compared to that of FSH and oestradiol concentration. Three groups of patients were studied: (i) patients who experienced cycle cancellation; (ii) patients who underwent oocyte retrieval; (iii) patients who were precluded from IVF due to elevated FSH concentrations. While FSH and oestradiol concentrations were statistically similar in groups 1 and 2, MIS concentrations were significantly lower in group 1. In group 2, MIS concentration positively correlated with the number of oocytes retrieved. In group 3, 91% had low or undetectable MIS concentrations. The results indicate that MIS concentration accurately predicts cycle cancellation that is belied by normal FSH and oestradiol measurements, and has a better correlation with the number of oocytes retrieved than FSH and oestradiol measurements.