- Abstract Background Obstructive sleep apnea syndrome (OSAS) is associated with long-term cardiovascular morbidity. Little is known about these relations at early stages. We conducted a case-control study in which we analyzed the clinical characteristics of young adults who underwent a periodic health examination and were screened for, and eventually found to experience, OSAS. Methods We identified 121 subjects newly diagnosed in a sleep study as having OSAS, and 229 matched control subjects in which screening for OSAS was negative. All had a medical interview, physical examination, and routine laboratory tests. Results Subjects who had OSAS had a higher, body mass index (3-kg/m 2 difference) and a higher diastolic blood pressure (4–mm Hg difference) value, without elevation in systolic blood pressure. There was no metabolic difference (lipids profile and fasting glucose levels) between groups. Conclusions Diastolic blood pressure is higher early in the course of OSAS. Long term follow-up may determine effects of prevention and early intervention in OSAS and associated hypertension.