Sleep apnea-hypopnea syndrome (SAHS) is characterized by recurrent episodes of hypoxia/reoxygenation, which seems to promote oxidative stress. SAHS patients experience increases in hypertension, obesity, and dyslipidemia, and the oxidative state has been related to the genesis of these disorders. The purpose of this study was to examine the changes in oxidative stress markers and metabolic parameters in S AHS patients after 1 month of treatment with continuous positive airway pressure (CPAP), in relation to their previous metabolic disorders. The study included 78 SAHS patients who required CPAP. The patients were classified according to their disorders, including hypertension, obesity, and dyslipidemia. Measurements were made before and after 1 month of treatment with CPAP. The diastolic blood pressure decreased after treatment in all the patients, significantly so in those who were nondyslipidemic, obese, or hypertensive (the systolic pressure also fell in these latter patients). Plasma oxidative stress biomarkers showed a significant antioxidant capacity and increased activity (P<0.05) after treatment, more so in the nondyslipidemic and hypertensive patients. Furthermore, serum lipid peroxidation levels decreased after CPAP (P<0.01). No change was observed in insulin resistance (IR) after CPAP treatment in any of the different disorders. In conclusion, oxidative stress markers improved significantly after CPAP treatment in SAHS patients, especially in the nondyslipidemic and hypertensive patients. Moreover, the blood pressure decreased after CPAP treatment, particularly in the obese, nondyslipidemic, and hypertensive patients. No significant change in IR was found in any of the SAHS patients after CPAP treatment.