Background . Serum lipoprotein (a) (Lp(a)) is an independent risk factor for premature coronary artery disease in Caucasians. Generally Lp(a) serum levels remain fairly constant throughout an individual's life, but are presumably modulated by sex hormones. This study documents the distribution and correlates of serum Lp(a) during sexual maturation in Belgian children. A comparison with Lp(a) levels in Belgian adults is made. Methods . Serum Lp(a), lipid and apolipoprotein A-I and B levels were determined cross-sectionally in 266 Belgian schoolchildren and adolescents in relation to sexual maturation, anthropometrics and socioeconomic status. Sexual maturity was scored according to Tanner's classification. Results . Median Lp(a) levels were 82, 117, 110, 100 and 73 mg/l at the five subsequent genital development stages in boys (ANOVA, P = 0.816), and 73, 78, 204, 110 and 114 mg/l at the five breast development stages in girls (ANOVA, P = 0.087). The Lp(a) distributions in boys and girls were skewed to the right, overall medians being 82 and 94 mg/l ( P = 0.2537). The 90th and 95th percentiles were 515 and 712 mg/l respectively. The geometric Lp(a) mean in children was significantly higher compared to that in 683 sex-matched Belgian adults (89 mg/l versus 69 mg/l, P = 0.006). Multiple linear regression pointed out that developmental age, chronological age, body mass index and/or systolic blood pressure predicted serum lipid and apolipoprotein levels, but none of the Lp(a) variance. Conclusion . Pubertal stage was not correlated with Lp(a) levels in Belgian schoolchildren, supporting the contention that serum Lp(a) is predominantly genetically controlled.