Azoospermia refers to the medical condition of a man not having any measurable level of sperm in his semen, and it's associated with very low levels of fertility. Italian researchers reported the case of a 34-year-old azoospermic man who had abused anabolic steroids. Fortunately, his spermatogenesis recovered close to normal six months after the cessation of steroid abuse and the administration of hormonal therapy. The investigators felt that their findings confirm the recovery of spermatogenesis after steroid abuse; however, they also noted that steroid abuse may have some adverse effects on the quality of sperm. Specifically, lab tests showed a high frequency of XY disomy in sperm. I won't even try to explain what that means, so one should consult a reproduction specialist if needed.

Reference: Moretti E et al. Structural sperm and aneuploidies studies in a case of spermatogenesis recovery after the use of androgenic anabolic steroids. J Assist Reprod Genet, 2007 Mar 8; [Epub ahead of print].