STUDY OBJECTIVES: The aim of this study was to verify the reliability and validity of the Spanish short version of the Functional Outcomes of Sleep Questionnaire (FOSQ-10SV) in Peruvian patients with obstructive sleep apnea (OSA). METHODS: Participants underwent physical examinations, completed the FOSQ-10SV, and polysomnography tests were carried out. RESULTS: A total of 672 patients were analyzed, 75 females (11%), mean age 50.5 ± 13.8 years. A total of 563 patients (84%) had OSA. The mean FOSQ-10SV score was 15.96 ± 3.23. The FOSQ-10SV Cronbach alpha was 0.84 and two significant factors were extracted in the factor analysis-both factors explained a variance of 43% and 14%. A significant correlation was found between the FOSQ-10SV score and the apnea-hypopnea index. Patients with more severe disease have a lower FOSQ-10SV score (P = .003). Ninety-nine patients with OSA who started continuous positive airway pressure treatment were followed, and we observed an improvement in the FOSQ-10SV score from pretreatment to posttreatment (P < .001). CONCLUSIONS: The FOSQ-10SV has internal consistency, construct validity, and the sensitivity to change in Peruvian patients with OSA who undergo treatment.