BACKGROUND: Although ooverweight and obesity are considered as a health problem that affects millions of people worldwide, the implication of socio-economic status (SES) in these healthy conditions have rarely been investigated. We evaluated the associations of overweight and obesity with SES, in a population based sample of Greek adults. METHODS: During 2001-2002 we randomly enrolled 1514 men (18-87 years old) and 1528 women (18-89 years old), stratified by the age-sex distribution (census 2001) of the Attica area, Greece. We studied several demographic, anthropometric, lifestyle, dietary and bio-clinical factors of the participants. SES (low, middle and high) was defined through the education and economical level of the participants. RESULTS: The prevalence of overweight and obesity was 53 and 20% in men, and 31 and 15% in women, respectively, while an increase in the prevalence of obesity was observed with progressing age. Both men and women in the higher SES group had significantly lower prevalence of obesity as compared to the middle and lower SES group (p<0.001). However, multivariate analysis showed that the observed associations between SES and obesity were mainly explained by differences in physical activity status and energy intake of the participants. CONCLUSION: Overweight and obesity seems to be a serious health problem, affecting more prominently people in the lower SES. However, eating and other lifestyle habits mainly explained the association between SES and obesity.