Basic method in the study of male infertility is the analysis of semen. This is often the first step in testing of infantile couple. Besides semen, if necessary, clinical and ultrasound examinations are performed by the urologist, as well as surgery, hormone tests, and testicular biopsy. In 2010 The World Health Organization has established new criteria for defining “normal” semen. Due to the complexity of the problem, it is recommended that the semen analysis is carried out in “referential laboratories”, possibly by reproductive embryologist, a specialist who deals with in vitro fertilization. The key parameters that are considered are the number, motility and morphology of sperm. Referential values for these parameters are approximate and we cannot say that men with normal results will surely be fertile, as well as the existence of lower semen of the following criteria automatically leads to infertility and the impossibility of spontaneous pregnancy. Yet, of all the parameters, the most important is the ability of sperm to fertilize an egg cell, and it is difficult to determine its possibility for fertilization by routine inspection. Parameter Old criteria (1999.) New criteria (2010.) volume 2 ml 1,5 ml Concentration 20 millions/ml 15 millions/ml Progressively movable 50% 32% Normal forms 14% 4% Based on these criteria, we distinguish between the following disorders: • Oligozoospermia – reduced concentration of sperm • Astenozoospermia – reduced sperm motility • Teratozoospermia – reduced percentage of normal forms of sperm Most commonly there is a disorder of all aspects of the quality of semen, and comes to the combination of pathological findings called Oligoasthenoteratozoospermia – OAT (reduced number, motility and percentage of morphologically correct forms simultaneously) which can vary from mild forms (OAT gr I) to more severe forms (OAT gr III). The most difficult case is a condition known as Azoospermia – absence of sperm in the ejaculate.