Chronic Obstructive Pulmonary Disease (COPD) and Obstructive Sleep Apnea (OSA) are separately associated with several comorbidities. The coexistence of the two diseases, referred to as overlap syndrome, may act as a predisposing factor for a higher prevalence of comorbidities compared to those associated with each disease separately. The objective of the study was to evaluate the relative prevalence of cardiovascular as well as other comorbidities, in patients with the overlap syndrome, as compared to patients that are diagnosed solely with OSA. We examined thirty-eight (38) patients (27 men, 11 women) with coexisting COPD and OSA - overlap syndrome (Group 1) vs. 38 patients with OSA-only (Group 2), matched for sex, age, and Body Mass Index (BMI). All patients underwent pulmonary function tests (PFTs), oximetry and overnight polysomnography and were asked about other coexisting chronic diseases and medications. The two groups differed significantly, as expected, in PFTs (Forced Vital Capacity - FVC, p=0.005, Forced Expiratory Volume in 1 s - FEV1, p<0.001) and in daytime oximetry (p=0.007). Three (3) overlap (7.89%) and 9 OSA patients (23.69%) had no other known diseases. All others suffered from 1 - ≥ 4 comorbidities. Overlap patients suffered more often from multiple (≥ 4) comorbidities than OSA-only patients (11, 28.95% vs. 4, 10.52%, respectively). The most common coexisting diseases were hypertension (50% vs. 42.1%), cardiovascular disease (CVD) (44.74% vs. 26.31%), diabetes mellitus (DM) (28.95% vs. 13.16%), dyslipidemia (21.05% vs. 26.31%) and depression (7.89% vs. 13.16%). We conclude that comorbidities, especially cardiovascular, in patients with overlap syndrome are at least as prevalent as in sleep apneic only patients and may contribute to the overall severity and prognosis of the disease.