The aim of this study is to assess the test-retest stability of the Spanish version of Youth Self Report after 18 mo. for a sample of 357 Catalonian high school students (158 boys and 199 girls). At Time 2 the girls' scores increased on Delinquent and Aggressive Behavior scales and, therefore on Externalizing scores. At Time 2 the boys' scores increased on Attention Problems and Delinquent Behavior and decreased on Anxious/Depressed, Social Problems, and Internalizing scales. Significant differences in the remaining scales were not observed. The test-retest intraclass correlations for the broad-band scales ranged between .62 (Internalizing) and .68 (Externalizing) and for the narrow-band scales between .37 and .67. The correlations for girls and boys were similar but slightly higher for girls on Anxious/Depressed and Thought Problems.