Abstract: BACKGROUND: In adolescents the temporal directionality to the asthma and adiposity association remains unclear. Asthma may be a consequence of obesity; however, asthma may increase adiposity. OBJECTIVES: This study aimed to assess the associations between (i) baseline weight status and subsequent asthma and (ii) baseline asthma and subsequent weight status after 4 and 11 years of follow-up (N = 1543 and N = 1596, respectively) using data from three, sequentially enrolled population-based surveys of Norwegians aged 12-30 years from 1995 to 2008. METHODS: Weight status was defined as general (body mass index) or abdominal (waist circumference) underweight, normal weight, overweight or obesity. Self-report physician-diagnosed asthma defined asthma status. RESULTS: Over the longitudinal 11-year follow-up, baseline generally overweight or abdominally obese adolescents had increased risk of asthma. Likewise, baseline asthmatics had increased risk of general overweight or abdominal obesity. After sex stratification, these associations were stronger in males. Generally (odds ratio [OR] 1.90; 95% confidence interval [CI] 1.32, 2.73) or abdominally (OR 1.66; 95% CI 1.13, 2.44) overweight males were at increased risk of asthma. Baseline asthmatic males were also at increased risk of general (OR 2.14; 95% CI 1.54, 2.98) and abdominal (OR 1.77; 95% CI 1.27, 2.47) overweight. CONCLUSIONS: Among Norwegian adolescents, a bidirectional association of asthma and adiposity was observed in males. Each baseline condition increased the risk of the other condition over time. No association was observed in females.