Objectives: To compare the response of polycythemia in terms of hematocrit decrease in patients treated with positive airway pressure (CPAP) versus patients not treated with CPAP. Methodology: Randomized, parallel-group, nonblinded, controlled clinical trial. Patients diagnosed with OSA in a respiratory polygraphy (RP) and who meet all the inclusion criteria and none of the exclusion criteria will undergo sleepiness and quality of life questionnaires, anthropometric measurements and blood tests and will be randomized to a CPAP treatment group or control group, maintaining this treatment for 12 months. A visit will be made at 12 weeks ,24 weeks and 52 weeks to check compliance with CPAP in the treatment group and to carry out questionnaires on physical activity and quality of life, anthropometric measurements, blood tests including hemoglobin and hematocrit as well as parameters related to coagulation and platelet function and changes in medication as well as adverse effects. Efficacy variables: blood count, hemoglobin, haematocrit, erythropoietin, mean corpuscular volume (MCV), mean corpuscular haemoglobin (MCH), mean corpuscular haemoglobin concentration (MCHC), mean platelet volume (MPV), platelets, coagulation, erythrocyte range of distribution (ADE), glucose, creatinine, glomerular filtration rate, aspartate aminotransferase (AST), alanine aminotransferase (ALT), gamma glutamyltransferase (GGT), Total bilirubin, hypoxic burden, Epworth score, EuroQol- 5D questionnaire.