Excessive erythrocytosis (EE) [hemoglobin (Hb) >21g/dl] observed in natives at high altitude (HA) seems to be due to elevated serum testosterone levels compared with men without EE at HA. The aim of the study was to determine the association between serum testosterone levels and high hemoglobin levels at HA with sperm quality. The study was conducted with 72 adult men living at 4340m and 52 native men at sea level (SL). At HA, men were grouped according to hemoglobin value (group 1:16-21g/dl or group 2: Hb >21g/dl). Hemoglobin and serum testosterone levels were evaluated. Sperm concentration, percentage of progressive sperm motility, percentage of normal sperm morphology, and markers of seminal vesicles function (corrected seminal fructose) and of prostate function (seminal zinc levels) were calculated. Serum testosterone levels were significantly higher in the group with EE (p<0.001). Progressive sperm motility in men with EE was lower than in the other group (Hb >16-21g/dl) and that of those at SL. Seminal pH, zinc levels and normal sperm morphology in men at HA were lower than at SL. At HA, a significant inverse relationship was observed between hemoglobin and progressive sperm motility (p<0.01). At SL, serum testosterone levels were directly related with progressive sperm motility, whereas at HA, no association was observed (p>0.05). No association between testosterone levels and corrected seminal fructose was observed in men with EE. In conclusion, low sperm motility was observed in men with EE despite elevated serum testosterone levels suggesting a resistance of sperm motility.© Georg Thieme Verlag KG · Stuttgart New York.