Objective: To describe the prevalence of overweight and obesity in the Spanish adolescent population and its relationship with the socioeconomic status, and to assess their body fat composition and compare these results with previous data from our own country. Design: Cross-sectional multicenter study conducted in five Spanish cities (Granada, Madrid, Murcia, Santander and Zaragoza) in 2000-2002. Subjects: 2,320 adolescents with complete set of anthropometric measurements, 1,192 boys and 1,128 girls. Measurements: Body mass index calculated from weight and height measurements, and body fat percentage calculated from skinfold thickness measurements. Results: Overweight + obesity prevalences were 25.69 and 19.13% in boys and girls, respectively. Overweight + obesity prevalence increased in boys from high to medium-low socioeconomic status categories (p = 0.015); meanwhile, there was not a significant effect of socioeconomic status in girls. In males, overweight + obesity prevalence changed from 1985 to 2000-2002 from 13 to 35% and in females from 16 to 32%. The rate of change in overweight + obesity prevalences seems to increase in the last years; from 0.88 (1985 to 1995) to 2.33%/ year (1995 to 2000-2002) in males and from 0.5 (1985 to 1995) to 1.83%/year (1995 to 2000-2002) in females. The rate of body fat percentage increase was similar between 1980 and 1995 and between 1995 and 2000 2002: 0.26 and 0.23%/year, respectively, at 13 years of age, and 0.16 and 0.17%/ year, respectively, at 14 years of age. Conclusion: We observed elevated overweight and obesity prevalences in Spanish adolescents, similar to those observed in other European countries. There is a significant inverse relationship between socioeconomic status and overweight + obesity, but only in boys. The rate of change in overweight prevalence in Spanish adolescents seems to increase, and the rate of increase of body fat percentage seems to be similar as in previous years. Copyright (C) 2005 S. Karger AG, Basel.