There have been numerous inconclusive studies examining the differences between unexplained and peritoneal endometriosis-associated infertility. Hence, the choice of artificial reproductive technique may be difficult. This prospective study compares outcome in couples with unexplained infertility and with minimal or mild endometriosis-associated infertility, undergoing treatment with ovarian stimulation combined with artificial insemination by husband. No differences were found between the unexplained infertile and the endometriosis group as to patient characteristics, response to ovarian stimulation and semen qualities. There was a significantly higher total pregnancy rate, with more multiple gestations, in the unexplained infertile compared with the endometriosis group. The difference in outcome could reflect differences in pathogenesis and aetiology for the two groups.