BACKGROUND AND OBJECTIVES: Although health risks associated to excessive body fat increase with small increases in body weight, measurement of body fat is usually grouped in very few categories. The aim of our study was to assess whether the risk for a combined end-point including the incidence of either hypertension and/or type 2 diabetes mellitus and/or the metabolic syndrome was elevated even within the "normal" limits of body-mass index (BMI). MATERIAL AND METHODS: We followed up 10,639 initially healthy university graduates participating in the SUN dynamic cohort for a variable period ranging 2 to 6 years. Baseline BMI and physical activity were the major exposures. The combined end-point was defined by the incidence of either hypertension and/or type 2 diabetes and/or the metabolic syndrome during the follow-up period. We fitted non-conditional logistic regression models and nonparametric regression models (restricted cubic splines). RESULTS: We observed 768 incident cases of the combined outcome (incidence of 16/1000 person-years) and found a monotonic linear association between BMI and the combined end-point. The multivariate-adjusted odds ratios for the combined end-point were 1.4 (95% CI: 1.1-1.7) for BMI 22-24.9 kg/m2, 2.7 (2.1-3.5) for 25-29.9 kg/m2 and 4.0 (2.8-5.6) for 30 kg/m2. We observed a threshold effect in the association between physical activity and the combined end-point multivariate-adjusted odds ratio=0.8 (0.7-0.9) for >15 METs-h/week. CONCLUSIONS: Our findings suggest that the incidence of metabolic risk factors (hypertension, diabetes mellitus and/or metabolic syndrome) is already increased at a BMI of 22 kg/m2 in young adults. These results deserve consideration for judging whether the cut-off point for "normal" weight should be lowered.