Background: Hyperhomocysteinemia has been accepted as an independent risk factor for atherosclerosis and atherothrombosis. In recent years, several reports have appeared in the literature linking the use of anabolic steroids with acute vascular events in bodybuilders. In this study, we investigated whether hyperhomocysteinemia could contribute to the high vascular risk in bodybuilders taking anabolic steroids. Methods and results: Twenty-three bodybuilders in different phases of their training cycle and six control athletes participated in our study. Anthropomorphic measures displayed a higher body mass index for bodybuilders in the competition phase than for bodybuilders in the work-out and build-up phases, and for control athletes. Homocysteine levels were 8.7+/-1.6 µmol/l (mean+/-S.D.) in control athletes, 8.5+/-2.8 µmol/l in work-out phase bodybuilders, and 8.3+/-1.5 µmol/l in competition phase bodybuilders, but 11.9+/-3.1 µmol/l in build-up phase bodybuilders (P<0.05 for build-up phase bodybuilders vs. control athletes, work-out phase bodybuilders, and competition phase bodybuilders, respectively). Vitamin B12 and folate levels did not differ significantly between the four groups. Conclusion: Our study shows that intake of anabolic steroids, as used typically by bodybuilders in the build-up phase, induces acute hyperhomocysteinemia and is likely to initiate an additional, potentially atherothrombotic mechanism in this group of athletes.