High incidence of infertility along with low vitamin D levels was detected in otherwise healthy young men. The aim is to observe the effect of vitamin D supplementation on semen parameters as assessed by semen analysis in infertile men. In total, 45 men (mean age 36.6 years) in consecutive order were included, of whom 34 finished the study. Subjects were supplemented by vitamin D (cholecalciferol) 2500 IU/day. Vitamin D levels were assessed by HPLC. Semen analysis was performed strictly following 2010 WHO guidelines. Study periods were baseline and month 6. During follow-up, 20 %, 7.4 %, 22 % and 0.7 % increase in serum vitamin D levels, progressive sperm motility, sperm concentration and sperm morphology, respectively, were observed (all p<0.05). At follow-up end, 9 patients (26 %) reached normal sperm parameters of whom 2 fertilized their partner. There was no correlation between vitamin D and semen parameters observed. This study proves that vitamin D supplementation is possibly a modulator of sperm parameters in vitamin D deficient, otherwise healthy men. Although a direct relationship between vitamin D and sperm parameters was not observed obtaining adequate vitamin D levels could likely play a role in the male factor of infertility.