The aims of this study were the Italian standardization of the Child Behavior Checklist (CBCL/4-18) and the Teacher's Report Form (TRF), the analysis of the internal consistency of the two instruments, and the evaluation of the agreement between parents' and teachers' ratings. A group of 1423 parents and 1464 teachers of children and adolescents aged 4 to 18 years, from three different provinces of Northern Italy, were randomly recruited. Boys scored higher than girls on the Externalizing scales on both CBCL and TRF, while there were no significant differences between the two sexes on the Internalizing scales. In general, internalizing problems increased with age, whereas externalizing behaviors decreased, mainly through a reduction of aggressive problems in older subjects. For most scales, low socioeconomic status was associated with high problem scores. Most scales of the CBCL and the TRF showed a satisfactory internal consistency, with higher α coefficients for overt behaviors. A low - to - moderate parents' and teachers' agreement was found, with the higher correlation found for the Attention Problems scale. Overall, the figures of this first standardization are in line with the results of most studies carried out in Western and Eastern countries, evidencing a good applicability of Achenbach's instruments in Italy.