This report examines the concurrent validity of different informant and self-report assessment instruments of psychopathology, both general and specific for anxiety and/or depression, in referred mentally retarded adolescents with a depressive and anxiety disorders, according to DSM IV criteria. A consecutive, unselected sample of 50 mildly and moderate mentally retarded adolescents (29 males and 21 females, aged 11.8 to 18 years, mean age 15.1) were assessed using standardized assessment techniques: Psychopathology Instrument for Mentally Retarded Adults (PIMRA) (informant version) (total score, affective and anxiety subscales), Child Behavior Checklist (CBCL) (informant version) (total score, internalizing and externalizing scores, anxiety-depression scale), Zung Self-Rating Depression Scale and Zung Self-Rating Anxiety Scale. Patterns of correlation among measures were calculated. PIMRA and CBCL total scores were closely intercorrelated. Internalizing and externalizing scores of CBCL were not intercorrelated, but they both correlated with CBCL and PIMRA total scores. Anxiety measures were positively correlated; they correlated with PIMRA and CBCL total scores, as well as with the internalizing score of CBCL. Depression measures were not correlated; their correlation with more general measures of psychopathology was weak. Clinical implications of these findings are discussed.