Background and objectives: Sociodemographic characteristics influence on effectiveness of adolescents' nutrition education . It is weak known how sociodemographic characteristics act on unhealthy dietary patterns in long-time perspective. Objective: Assessment of the effect of nutrition education program on unhealthy dietary pattern in sociodemographic context after 9-month follow-up in Polish adolescents. Methods: The prospective study involved 464 adolescents aged 11-13 years at baseline. Eating habits were assessed based on frequency food consumption. A non-healthy diet quality index (nHDI) including 4 foods (fast foods, sweetened beverages, energy drinks, sweets) was analysed (range: 0-100 points). After 9-month follow-up changes in nHDI were compared between 'educated' (n=319) and... 'control' (n=145) groups and analysed in subgroups: boys/girls, rural/urban residence, bottom/middle/upper tertile of family affluence scale (FAS) . Results: After 9 months the mean changes in nHDI between 'educated' and 'control' groups were significant in boys and urban subsample. In boys the mean nHDI was lower by 0.9 points in 'educated' and higher by 2.0 points in 'control' group. In girls the mean increase in nHDI was insignificantly lower in 'educated' than 'control' group (by 0.4 and 2.3 points, respectively); in rural subsample the mean decrease was insignificantly higher (by 0.9 and 0.5 points, respectively); in urban subsample the mean increase in nHDI was significantly lower in 'educated' than 'control' group (by 0.2 and 4.0 points, respectively); in bottom FAS tertile the mean increase in nHDI was insignificantly lower in 'educated' than 'control' group (by 2.1 and 4.6 points, respectively); in upper FAS tertile the mean decrease in nHDI was insignificantly higher in 'educated' than 'control' group (by 2.1 and 0.1 points, respectively). Conclusions: The strong effect of one-time nutrition education episode in reducing unhealthy dietary pattern in Polish adolescents in long-time perspective was shown in boys. For girls a special attention should be paid in designing nutrition education.