Finasteride is a specific inhibitor of the 5alpha reductase enzyme originally approved for the treatment of benign prostatic hypertrophy and also for the treatment of androgenetic alopecia (AGA) in men at a dose of 1 mg/day. We report on three cases of young men recruited at our Centre for Male Infertility who had used finasteride for five years. Semen quality was investigated by light microscopy to evaluate sperm concentration and motility. Sperm morphology was performed by transmission electron microscope (TEM) and the data were analyzed. The presence of Y microdeletions was investigated by PCR. Meiotic segregation was explored by fluorescence in situ hybridization (FISH). Patient 1 was azoospermic, patients 2 and 3 showed a normal sperm concentration and severely reduced progressive motility. TEM analysis revealed altered sperm morphology consistent with necrosis and FISH data revealed elevated diploidy and sex chromosome disomy frequencies. This examination was repeated 1 year after the men had suspended the use of finasteride, without receiving any other treatment. A recovery of spermatogenetic process was observed. Motility and morphology improved whereas the meiotic pattern did not change presenting elevated diploidy and sex chromosome disomy frequency.