Objective: Altered utero-ovarian blood flow has been claimed to be a subtle cause of unexplained infertility. The aim of this study was to compare between the flow velocity indices in the uterine and ovarian arteries during the luteal phase in fertile and unexplained infertility women. Study design: Observational, cross section, controlled study done at the departments of Obstetrics and Gynecology, Benha Faculty of Medicine, Egypt, during the period from October 2010 to October 2011. Patients and methods: Two groups each of 30 cases and aged 20-25 years were studied. A control group of fertile women who got pregnant within one year of marriage, and a study group of women with unexplained infertility were included. Trans-vaginal pulsed color Doppler ultrasound was done at days 21–23 of the cycle to measure uterine and ovarian arteries resistance and pulsation indices. Outcome measures: Mean uterine and ovarian arteries resistance and pulsation indices in both groups and their values in the diagnosis of altered blood flow in unexplained infertility were measured. Results: Women with unexplained infertility had significantly higher uterine and ovarian arteries pulsation index (P