Introduction Obstructive sleep apnea (OSA) is associated with high cardiovascular risk. Carotid intimae media thickness (cIMT) is a surrogate marker of subclinical atherosclerosis. Circulating adipocyte fatty acid-binding protein (FABP4) levels have been associated with metabolic alterations and increased cardiovascular morbidity. Our aim was to evaluate circulating FABP4 concentrations and cIMT in OSA patients. Materials and methods We included 125 participants, aged 18–75, referred by suspected OSA to our Sleep Disorders Unit. OSA was assessed by overnight polysomnography (PSG). Circulating FABP4 levels were determined by ELISA and cIMT was measured by ultrasonography. Results Circulating FABP4 levels were higher in the presence of OSA (25.8 ± 9.7 vs. 19.1 ± 7.9 μ g/l, p = 0.003) and according to OSA severity (overall p = 0.017). The presence of atheromatous carotid plaque as well as cIMT mean values were both higher in OSA compared to non OSA participants (48% vs. 2%, p = 0.004 and 665.4 ± 120.1 vs. 581.3 ± 78.1 μ m, p = 0.005, respectively). cIMT did not differ between OSA severity groups. Moreover, FABP4 levels were positively correlated with cIMT (r = 0.341, p 0.001). Conclusion FABP4 is associated to OSA presence and severity. FABP4 is a biomarker of metabolic comorbidities in OSA patients. The carotid ultrasonography in these patients can reliably report of the precociousness of arteriosclerotic phenomenon. However, more studies are needed before this technique is widespread in our sleep units. Acknowledgements SOCAP, SEPAR and CIBERDEM.