We investigated the tracking phenomenon of serum lipoprotein (a) concentrations and assessed the impact of serum concentration of lipoprotein (a) cholesterol on total cholesterol concentrations in children from 7 to 36 months of age. Serum samples for lipoprotein (a) and cholesterol determinations at 7, 13, 24 and 36 months were prospectively obtained from 430 children. Serum lipoprotein (a) was determined using immunoradiometric assay. A strong correlation was observed between lipoprotein (a) concentrations at 7 and 36 months of age (r = 0.88, P < 0.001). Seventy-eight per cent to 86% of the children in the lowest and highest lipoprotein (a) quintiles at 13 months remained in the respective quintiles at 36 months. The average contribution of lipoprotein (a) cholesterol to total cholesterol varied from 0.5% to 3.2% (individual variation 0.13-32.39%) depending on the type of milk received and the age of the children. At 7 months the contribution was 0.44% in breast-fed and 0.93% in formula-fed infants (P < 0.0001). The tracking phenomenon of serum lipoprotein (a) concentrations is strong already in early childhood. The contribution of lipoprotein (a) cholesterol to serum total cholesterol concentration should be taken into account when the changes in serum cholesterol levels are interpreted in the first year of life.