Objective: To assess tracking of energy and nutrient intakes between adolescence and young adulthood. Design: Longitudinal study of a random sample of adolescents (aged 15 years at baseline). The extent of tracking of dietary intakes (assessed by diet history) was investigated using weighted kappa statistics (kappa). Setting: Northern Ireland population survey. Subjects: Adolescents who participated in the Young Hearts Project, Northern Ireland at age 15 years, and subsequently at young adulthood aged between 20 and 25 years (n=245 males, n=231 females). Results: Despite overall increases in height and weight (both P < 0.001), increases in body mass index in males (P < 0.001) and body fatness in females (P < 0.001), median reported intakes of energy (kJ kg(-1) day(-1)), carbohydrate (g day(-1)) and fat (g day(-1)) decreased (all P < 0.001) over time. Expressed as nutrient densities (per MJ), diets at young adulthood were overall richer in thiamin, vitamin B-6, total folate (all P < 0.001), vitamin C (P < 0.01) and vitamin D (P < 0.05). Whereas the nutrient density of the males' diets decreased over time for calcium (P < 0.05) and vitamin A (P < 0.001), iron and riboflavin densities increased in the females' diet (P < 0.001). Tracking of energy (MJ day(-1)) and nutrient intakes (expressed per MJ day(-1)) at the individual level was only poor to fair (all kappa < 0.25), indicating substantial drift of subjects between the low, medium and high classes of intake with increasing age. Conclusions: These data suggest that individual dietary patterns exhibited at 15 years of age are unlikely to be predictive of dietary intakes at young adulthood.