In 250 cases of sterility (no conception) or infertility (termination of pregnancy before viability) in which a pregnancy could be achieved, the pathological findings and the different treatments have first been analyzed. Subsequently the causes of impaired fertility were discussed. The difficulties to investigate distinct reproductive functions and to recognize definite causes of barrenness by correct interpretation of data are pointed out. On the basis of a critical evaluation of our findings the most frequent factor responsible for the initial sterility or infertility may have been disturbed ovarian function, followed by seminal disorders and abnormal conditions concerning tubes and peritoneum. It seems noteworthy that only 1/3 of our cases revealed a more or less clear cause and in almost 1/4 of the cases later becoming pregnant the cause of impaired fertility remained undetectable.