The proportion of overweight children and adults has been growing rapidly in the last few years in many European and other countries. Certain consequences of overweight are already manifested in youth; in adulthood they are one of the main causes of death and several diseases. The study examined the proportion of overweight and obese Slovenian girls aged 7 to 18 with the use of an annually repeated cross-sectional study. The study lasted from 1991 to 2006 and was based on the body mass index according to IOTF norms. The results show that in this period the proportion of overweight girls increased by almost 30% (from 13.5% to 18.8%), whereas the proportion of obese girls doubled (from 2.3% to 4.6%). The prevalence of overweight and obesity is highest in childhood and early adolescence where it is around two to three times higher than at the age of 18.