Sterility in the male is an exceedingly complex subject entailing exhaustive urologic, endocrinologic and laboratory studies. For the purpose of simplification, all cases can be divided into two groups, urologic and endocrinologic. Occasionally malnutrition or vitamin deficiency may cause sterility, but it occurs so infrequently that for practical purposes it need not be stressed. The paper is limited to the study of sterility as it affects the human being, as the result of current animal experimentations are not analogous to those found in man. The urologic cases are classed as either congenital or acquired, depending on the etiology. The most frequent congenital causes of sterility are hypospadias, cryptorchism and abnormal attachment of the epididymis to the testicle. The majority of acquired cases are the result of a former gonorrheal infection resulting in bilateral epididymitis, stenosis of the ejaculatory ducts, seminal vesiculitis, vasitis and urethral stricture. The endocrinologic cases are due