An accurate interpretation of information obtained from multiple assessors is indispensible when complex diagnoses of behavioral problems in children need to be confirmed. The present study examined the similarity of parents and kindergarten teachers ratings on children’s behavior in a sample of 160 preschool children (a clinical group including 80 children with externalizing behavioral problems and a matched control group including 80 children). Behavioral problems were assessed using the SDQ, and the DISYPS-II questionnaires for ADHD and conduct disorders. The results revealed low levels of parent-teacher agreement for their ratings on the children’s behavior in both groups with the highest correlations in the non-clinical sample. Parent-teacher agreement did not differ significantly across the samples. Parent and teacher ratings correlated with the prevalence of externalizing disorders and were found to be almost independent of each other. The results highlight the importance of multiple informants and their independent influence within the diagnostic process.