OBJECTIVES: To examine whether involvement in food preparation tracks over time, between adolescence (15-18 years), emerging adulthood (19-23 years) and the mid-to-late twenties (24-28 years), as well as 10-year longitudinal associations between home food preparation, dietary quality and meal patterning. DESIGN: Population-based, longitudinal cohort study. SETTING: Participants were originally sampled from Minnesota public secondary schools (USA). SUBJECTS: Participants enrolled in Project EAT (Eating Among Teens and Young Adults)-I, EAT-II and EAT-III (n 1321). RESULTS: Most participants in their mid-to-late twenties reported an enjoyment of cooking (73 % of males, 80 % of females); however, few prepared meals including vegetables most days of the week (24 % of males, 41 % of females). Participants in their mid-to-late twenties who enjoyed cooking were more likely to have engaged in food preparation as adolescents and emerging adults (P < 0·01); those who frequently prepared meals including vegetables were more likely to have engaged in food preparation as emerging adults (P < 0·001), but not as adolescents. Emerging adult food preparation predicted better dietary quality five years later in the mid-to-late twenties, including higher intakes of fruit, vegetables and dark green/orange vegetables, and less sugar-sweetened beverage and fast-food consumption. Associations between adolescent food preparation and later dietary quality yielded few significant results. CONCLUSIONS: Food preparation behaviours appeared to track over time and engagement in food preparation during emerging adulthood, but not adolescence, was associated with healthier dietary intake during the mid-to-late twenties. Intervention studies are needed to understand whether promoting healthy food preparation results in improvements in eating patterns during the transition to adulthood.