Purpose Investigating tracking of selected health behaviours from adolescence into adulthood. Sample Data were collected by questionnaires in a longitudinal study from age 15 to 33 in Oslo, Norway, including 443 (53% women) ethnic Norwegians participating in 1981 (baseline), 1991 and in 1999. Measures At baseline and in 1991 sugar and fruit/vegetable intake was computed as scores, grouped into three; low, medium and high, while in 1999 this intake was computed as grams/day. Physical activity (PA) at baseline and in 1991 was grouped as exercising < weekly, once weekly, and ≥ twice weekly, while the dependent PA-variable was proportion exercising ≥ twice weekly. Smoking was grouped as never, occasionally and weekly at baseline and daily smoking versus no smoking was reported for 1991 and 1999. Results A consistent tracking pattern was seen from 1981 (age 15) to 1991 (age 25). Comparing highest versus lowest sugar-intake tertile at baseline, the scores in 1991 were (mean) 5.0 versus 4.0 (p<0.001) for gender combined. For fruit/vegetables the scores within highest versus lowest baseline tertile were 11.4 and 10.3 (p=0.008). The proportion who exercised ≥ twice weekly in 1991 among the most versus the least frequent exercisers at baseline, were 53.1% and 32.6%, (p=0.002), and the proportion smokers was 78.0% among baseline smokers compared to 32.7% (p<0.001) among never-smokers. A similar pattern emerged within the adult age-range (25 � 33 years). However, comparing 1981 and 1999, the prediction power of 1981-data for behaviour in 1999 was weaker. Conclusions Results from this study indicate a substantial degree of tracking of health-related behaviour from adolescence into adulthood.