- Background: The aim of this study was to evaluate the change in prevalence of weight disorders and associated morbidity among young adults. Methods: Records of 1 021 211 subjects aged 17, who underwent a medical examination, were included. Results: Among female subjects the prevalence of underweight increased steadily from 13.2% to 15.6%. No statistically significant trend was found among male subjects. Among male subjects a twofold increase in the prevalence of obesity was observed, while among female subjects there was an increase of 57%. In obese versus normal-weight male subjects the OR, adjusted for origin, education and year of recruitment, of having high blood pressure, diabetes type 2 and type 1 and hyperlipidemia were 4.1 (95%CI 3.89–4.34), 5.56 (5.09–6.07), 1.00 (0.30–3.27) and 16.07 (8.29–31.15), respectively. For obese female nominees the OR were 5.56 (95%CI 5.09–6.07), 4.42 (3.90–5.00), 3.59 (0.77–16.87) and 9.00 (4.36–18.60), respectively. Conclusion: A significant increase in prevalence of obesity was observed with an increased risk of having diabetes type 2, hyperlipidemia and high blood pressure. An increase in the prevalence of being underweight was observed in female subjects. Policy makers have to plan appropriate effective interventions that will promote a healthy lifestyle in adolescents and reduce obesity on the one hand, and avoid the fashion for being underweight, with its possible development to anorexia, on the other.