Introduction: Plasma viscosity (PV) constitutes an independent important predictor of initial and recurrent cardiac events and mortality. It has been suggested that there is a geographical variation in PV values related to coronary event rates. Little information exists regarding PV in Spain. Therefore, our objective was to determine PV in a large sample of randomly selected subjects from the Spanish population and to study which demographic or cardiovascular risk factors (CVRF) influence levels of PV in this population. Materials and methods: 1277 subjects (503 males, 774 females) aged 43 14 years (range: 20-70) were randomly selected from an Eastern Spanish population. These subjects were free of cardiovascular diseases and other major diseases. PV was measured at 37 C by means of the Fresenius GmbH plasma viscosimeter. In addition, total cholesterol, triglycerides, glucose and fibrinogen were measured. Results: In the crude analysis, no differences in PV were observed regarding gender (males: 1.235 +/- 0.061 cP; females: 1.236 +/- 0.059 cP, P=0.952). Women older than 50 years showed higher PV:1.248 +/- 0.057 cP than those aged less than 50 years: 1.232 0.059 cP, P=0.001. No differences in PV by age groups were observed in men (P=0.842). Furthermore, we evaluated the prevalence of the following CVRF: hypercholesterolemia, hypertriglyceridemia, hypertension, diabetes, tobacco smoking, obesity, and high fibrinogen levels. Prevalence of these factors was: 28%, 4.3%, 8%, 2.3%, 33%, 8.8% and 15% respectively. As some of these CVRF were correlated with PV levels, we carried out a multivariate analysis to adjust PV levels for the potential confounding effect of each one of these factors. After multivariate adjustment, PV was positively associated with high fibrinogen (> 320 mg/dL) levels in both men and women (P < 0.001). In addition, in women, but not in men, PV levels were independently associated with obesity (P < 0.001) and hypertriglyceridemia (P=0.01). After the multivariate adjustment, the association between PV and age older than 50 in women did not remain statistically significant, revealing a confusing effect of the CVRF in the crude analysis. (c) 2006 Elsevier Ltd. All rights reserved.