Obesity is a rapidly spreading endemic in almost every country of the developed world, of which Hungary is no exception. By a joint research project we aim to deepen our understanding of obesity-associated, and especially obesity-predicting changes of clinical markers (anthropometric indices, body composition, laboratory results etc.) in children, especially in teenage population. This paper presents the preliminary results of our investigations which pertain to obesity-related alterations in routine blood test parameters. For that end, we examined 340 healthy and obese children. Results show that there are differences between the routine laboratory parameters of obese and healthy subjects that are both statistically significant and medically interesting. We point out these differences in a statistically precise way, and show a method which can be efficiently used to classify children based on their laboratory parameters. This result can be used later to develop a more realistic model to predict the risk of obesity.