Objectives: This study aimed to assess the influence of coasting duration on the number and quality of oocytes and fertilization rate in male factor infertile women and those with polycystic ovary syndrome (PCOS). Methods: In this prospective observational follow-up study, 114 patients undergoing coasting (53 women with male factor infertility and 61 women with PCOS) were evaluated at the Royan Institute Research Center, Iran, between 2010 and 2012. Results: The results were analyzed according to the coasting periods of 1–4 days. In normal females, the number of oocytes retrieved was significantly reduced after the second day (p = 0.004). In addition, a statistically significant drop was observed in the number of metaphase II oocytes and fertilization rate after the third day (p = 0.006 and p = 0.006, respectively). No significant differences were observed in the number and quality of oocytes retrieved and fertilization rate with regard to coasting days in PCOS patients. Conclusion: Coasting with duration of more than three days should be performed with caution in normal females who are at risk of developing ovarian hyperstimulation syndrome.