OBJECTIVE: Description of the relationship between the overweight man and the reduction of his reproductive potential. DESIGN: Review article. SETTING: Center of Assisted Reproduction Sanus, Jihlava. METHODS: Approximately 15% of couples are trying to get pregnant unsuccessfully. In order to better assess the possible causes of this failure, it is vital to take into consideration the influence of owerweight and/or obesity in both men and women. Reduction of the reproductive potential of obese men occurs due to changes in hormonal levels regulating spermatogenesis, increased temperatures in the testicles, environmental toxins accumulated in adipose tissue, increased levels of oxidative stress as well as a higher incidence of erectile dysfunction. The likelihood of pregnancy is reduced even in the case of assisted reproduction methods. CONCLUSION: Obesity or overweight causes reduced fertility of men and often significantly prolongs the time required to achieve pregnancy. Prior to applying treatment for infertility, we assess all possibilities to increase the reproductive potential of overweight men. Significant weight loss in obese men results in regulated hormonal levels, moreover, in most cases, this leads to improved spermiogram parameters with increasing chances of getting pregnant.