BACKGROUND Although certain studies report high levels of vascular endothelial growth factor (VEGF) in obstructive sleep apnea syndrome (OSAS), the effect of systemic hypoxia on circulating VEGF remains controversial. OBJECTIVES To study the association of serum VEGF and OSAS in a large group of patients. METHODS One hundred patients with OSAS (mean age 58.1+/-12.4 years, mean body mass index 30.6+/-5.4 kg/m2) were tested for serum VEGF levels, and the findings were correlated with the severity of OSAS, as determined by the apnea-hypopnea index (AHI) on the basis of polysomnography and background data. RESULTS The mean AHI was 40.0+/-21.2 (range 10-106). Mean minimal oxygen saturation was 80.6+/-11.7% (range 43-98%) and mean time of oxygen saturation under 90% was 50.0+/-75.0 min (range 0-300 min). The mean VEGF level was 445.2+/-289.8 pg/ml in the study group (vs. 280 pg/ml reported in normal controls). The mean platelet count was 233.8+/-64.4 10(3)/ml and the mean VEGF/platelet ratio was 1.95+/-1.40 pg/10(6). There was no association of VEGF or VEGF/platelets with the severity of OSAS. However, both factors showed a significant correlation with patient age (r=0.224, p=0.01 and r=0.425, p=0.01, respectively). Age was the only parameter to significantly predict VEGF and VEGF/platelets on multivariate analysis (R2=0.713, p=0.001 and R2=0.844, p=0.001, respectively). CONCLUSION The elevation of serum VEGF in OSAS is not associated with the severity of the disease, but it is associated with patient age. VEGF might be involved in the long-term adaptive mechanism in OSAS, and its age-dependent increase might partly explain the reduced mortality in elderly OSAS patients.