Objective: Treatment of infertility needs classification of data from different centers. So we have decided to study infertility and its causes in this center.Material and Method: 1846 couples were clinically studied.Design: Retrospective analytic study method of infertile couples from 1998-2000 in Mashhad University.Result: Gaining enough information about infertility and its causes and effects is the first step in programming to cure infertile patients. Studying the infertility causes in the infertility center of Mashhad University was carried on for two years.This retrospective and descriptive study has been conducted on the basis of questionnaires filled out according to collected information from a number of infertile couples.From 1946 infertile couples, 82% of them were suffering from primary infertility while 18% of them had the problem of secondary infertility.In 39% of these couples, female infertility, 35% male infertility, 13% multifactorial causes and in 13% unexplained infertility factors could be seen.In evaluating, different causes of infertility in women in 48.9% of patients ovulatory factors, in 34.2% tubal factors, In 9% cervical factors. in 4.5% pritoneal factors, in 3.3% uterin factors and in 0.2% vaginal factors played the most important role.The same study carried on about male patients proved that, in 67% of them seminal abonormalites, in 30% varicocele, and in 4% retrograde ejaculation could be seen.And infertility with multifactorial causes which can be traced in 13% of patients. 61% of them suffered from ovarian factors, 29% from male and endocrin factors, 6% from male and cervical factors and 3% from male and tubal factors. Conclusion: Primary infertility is more common than secondary infertility P<000. But the rate of infertility between men and women is equal. In female infertility cases ovarian factors form the most common cases while in male infertility cases the rate of varicocele factors is 30% which is the most common. This study showed that in multifactorial cases, ovarian and male factors form the most and male and tubal factors are the least common cases.