Males with obstructive sleep apnea syndrome (OSAS) may present decreased testosterone serum levels because of hypoxemia. AIM: To correlate testosterone levels in OSAS patients with laboratory parameters. MATERIAL and METHODS: 103 registries of OSAS patients were reviewed from 2002 to 2009. The following data collected: age when polysomnography was done, hematocrit and hemoglobin levels, total testosterone serum levels, BMI, apnea/hypopnea index (AHI), and O2 saturation. STUDY DESIGN: A cross-sectional retrospective case study. RESULTS: 79 patients (77%) had no hormonal changes, and 24 patients (23%) had decreased serum levels. In patients with normal testosterone levels, 70% were overweight; 63% with altered testosterone levels had obesity grade I (p<0.05). Patients with altered testosterone levels had significantly lower average doses of Ht, Hb and androgen compared to patients without altered androgen levels. The average BMI of patients with altered hormone levels was significantly higher compared to patients with normal hormone levels. CONCLUSIONS: The relationship between morning testosterone levels and obesity, and to a lesser degree age, AHI and hypoxemia may be the cause of central suppression of testosterone in these patients. Decreased blood HT and HB levels may be related to lower levels of circulating testosterone.