BACKGROUND: There are large socioeconomic disparities in food behaviours. The objective of the present study is to longitudinally explore socioeconomic disparities in adolescents' fruit and vegetable (FV) intake and to assess mediators of the disparity. METHODS: A longitudinal study containing 896 adolescents from 20 randomly selected elementary schools within two Norwegian counties (response rate 84%). Questionnaires were administered in May 2002 (mean age 12.5 years) and again in May 2005. FV intake was measured by four food frequency questions (times/week). Socioeconomic status was based on parents' reports of their own educational level and family income (both dichotomized). Data were analysed with repeated mixed models. RESULTS: A disparity in adolescents' FV intake was observed with family income (1.1 times/week, P = 0.05). An interaction between parental education and time (survey) was found for parental education (P = 0.04) and the educational disparity was greater in 2005 (2.4 times/week, P