Childhood overweight (body mass index (BMI)>90th centile) poses a major public health problem in so far as adult diseases manifest themselves already during childhood. In this review, after examining the prevalence of metabolic and cardiovascular diseases, the issue of whether BMI or other clinical parameters are valid tools to predict co-morbidities in children is discussed. Data of 2001-2008 are reviewed, including several studies conducted on more than 260,000 overweight and obese children in Germany and Switzerland. Apart from non-metabolic co-morbidities, namely musculoskeletal complications and attention deficit/hyperactivity disorders in up to 74% and up to 58% of overweight children, respectively, at least one cardiovascular and metabolic risk factor was seen in 52% of the overweight children, mostly high blood pressure (35%) with increased left ventricular mass or arterial stiffness. Signs of fatty liver disease or dyslipidemia were found in up to 29 and 32% of the children, respectively. Type 2 diabetes was found in less than 0.7% of the children, and an elevated fasting glucose or glucose intolerance in 3%. Irrespective of BMI, the quality of fat and protein intake predicted hypertension or insulin resistance, and fructose predicted lower (and more atherogenic) particle size of low-density lipoprotein-cholesterol. Out of the adiposity markers, waist circumference was closely correlated with insulin resistance and the components of the metabolic syndrome. In conclusion, risk factors are found in more than half of the overweight children, most frequently high blood pressure or dyslipidemia, and were mainly related to waist circumference, but also to BMI and fat mass. Even in the presence of normal BMI, screening for cardiovascular risk factors is advocated in each child with elevated waist circumference, but its cut-off points still remain to be validated. The increased occurrence of orthopedic and psychiatric complaints may detrimentally influence health-related lifestyle and obesity therapy.