: OBJECTIVES. Although relatively little information exists concerning bone mineral density (BMD) in men, it has been demonstrated that similarly to observations in women, BMD decreases also with age in men, although to a smaller extent, and osteoporosis is increasingly recognized. Most reports concentrate, however, on men of advanced age. Therefore, we decided to investigate BMD in young healthy volunteers and in young patients suffering from infertility, and to compare it with serum tes-tosterone levels. MATERIAL AND METHODS. The study was performed on 80 men divided into two groups. The first group consisted of 39 young healthy men (mean age 22.1+/-0.3 years; range 20-29). The second group consisted of 41 infertile men with oligozoospermia (mean age 28.0+/-0.5 years; range 23-34). Serum testosterone levels and BMD were measured in each subject. RESULTS. Decrease in BMD (T-score below -0.3) was observed in 35.9% of the subjects in the group of young healthy men and in 60.9% of the subjects in the group of infertile patients. Among these numbers -penia (T-score between -1 and -2.5) was found in 4 subjects (10.3%) in the group of young healthy men and in 13 subjects (31.7%) in the group of infertile patients. There was a positive correlation between testosterone concentrations and BMD as well as T-score both in healthy subjects and in infertile patients. CONCLUSION. Results of the present study indicate that attention should be paid to testosterone deficiency in the young age in terms of the potential risk of decreased bone mineral density in the advanced age.