Body Mass Index (BMI) and skinfolds are common indicators of adiposity. Many studies have shown relationships between the BMI in childhood and adolescence and the BMI in adulthood. Similar correlations were observed for the skinfolds, although they tend to be lower. The aim of this study was to estimate changes with age in the genetic variance and heritability of the BMI and skinfolds among Polish twins born between 1959 and 1965. Observations involved male and female monozygotic (MZ) and dizygotic (DZ) twins, who were measured annually between 8 and 18 years of age. Body Mass Index and skinfold thicknesses at the triceps (TSF), subscapular (SSF) and suprailiac (SIF) sites were measured. Genetic variance and heritability were estimated for individual skinfold thicknesses, the sum of three skinfolds (SUMSF) and BM, separately by age classes for both sexes. Intraclass correlations were significantly higher for MZ twins than for DZ twins in both sexes and across all ages. Heritability estimates were significant for all indicators of adiposity, but varied with age and had different ranges for boys and girls. Estimates of genetic variance were significant for all indicators of adiposity and were higher for girls than for boys.