An epidemiological sample of 936 Dutch children originally aged 4-11 years was assessed at 2-year intervals over a 6-year period. Parents completed the Child Behavior Checklist (CBCL) on all four occasions. Stability coefficients computed for eight CBCL syndromes, Internalizing and Externalizing dimensions, and total problems revealed considerable long-term stability. There was no significant difference in the 6-year stability of internalizing vs. externalizing scores. This finding was at odds with reports of considerably lower stability of internalizing behavior, and was consistent with findings suggesting that the stability of internalizing problems should not be underestimated. The magnitude and specificity of the long-term stability of internalizing and externalizing scores lends support to the validity of these behavioral dimensions as tapped by the CBCL. No significant sex or age differences in the stability of problem behaviors were found.