Levels of vitamins A, E, C, B1, B2, B6, B12, folate and beta-carotene were assessed in plasma or whole blood in a group of 114 healthy adults. Biochemical vitamin status was classified into acceptable or suboptimal (moderate or severe). The independent association of various factors with the finding of a suboptimal vitamin status was studied by means of logistic regression analyses. Seventy seven per cent of subjects had suboptimal vitamin status for vitamin B2, 20% for vitamin A, and 84% for beta-carotene. Although few subjects had suboptimal biochemical levels for vitamin E, plasma levels of this vitamin were significantly lower in smokers than in non-smokers (p < 0.01). Likewise, plasma folate levels were significantly related to body mass index and the season of blood sampling (p < 0.05). Old age was protective (OR 0.15; 95% CI 0.03-0.67), whereas current smoking was harmful (OR 3.63; 95% CI 1.09-12.1) for riboflavin status. Age group of 25-59 years was independently associated to a low risk of suboptimal vitamin A status (OR 0.29; 95% CI 0.09-0.88). On the other hand, female sex had a negative effect on plasma vitamin A levels (OR 2.39; 95% CI 0.82-6.92) and smoking had a harmful effect on biochemical beta-carotene status (OR 2.72; 95% CI 0.82-8.99). This cross sectional study provides information about the determinants of vitamin inadequacy, and may be the basis for further pathophysiological studies.