During the fertile window of a woman's menstrual cycle, the effect of impending timed intercourse (TI) on the psychological well-being and behavior of male partners has not been thoroughly investigated, despite the fact that men comprise one half of each couple endeavoring to achieve natural conception. This prospective study consisting of 439 men was conducted during a 3-year period between July 1, 2008, and June 30, 2011. Various characteristics were evaluated, including newly acquired erectile dysfunction (ED); extramarital sex (EMS); intake of soft drinks (SD); levels of hormones, such as follicle-stimulating hormone (FSH), luteinizing hormone (LH), testosterone (T), prolactin, and estradiol (E2); and semen parameters. A total of 188 men (42.8%) experienced ED and 47 men (10.7%) engaged in EMS. As the number of TI episodes increased, the number of men with ED and EMS and those who wanted to avoid TI also increased (all, P , .0001). All 47 men who reported EMS experienced ED with their spouses. Men who consumed SDs produced significantly smaller volumes of semen (P 5 .0363). Among the hormones investigated, the levels of LH, T, and E2 were significantly lower in men with ED (all, P , .05) whereas the level of FSH was higher in contrast to E2, which was significantly higher in men who had EMS (both, P , .01). TI imposes a great deal of stress on male partners evoking ED and, in some cases, causing these men to seek EMS. Physicians and clinicians should acknowledge the potential harmful effects of TI on men. Furthermore, both female and male partners should also be cautioned about the increased possibilities of ED and EMS as TI incidents increase.