Multilevel confirmatory factor analysis was used to evaluate the factor structure underlying the 12-item, three-factor "Interagency Collaboration Activities Scale" (ICAS) at the informant level and at the agency level. Results from 378 professionals (104 administrators, 201 service providers, and 73 case managers) from 32 children's mental health service agencies supported a correlated three-factor model at each level and indicated that the item loadings were not significantly (p greater than 0.05) different across levels. Reliability estimates of the three factors (Financial and Physical Resource Activities, Program Development and Evaluation Activities, and Collaborative Policy Activities) at the agency level were 0.81, 0.60, and 0.72, respectively, whereas these estimates were 0.79, 0.82, and 0.85 at the individual level. These multilevel results provide support for the construct validity of the scores from the ICAS. When the ICAS was examined in relation to Level 1 and Level 2 covariates, results showed that participants' characteristics (i.e., age, job role, gender, educational level, and number of months employed) and agency characteristics (i.e., state location and number of employees) were not significantly (p greater than 0.05) related to levels of interagency collaboration. (Contains 4 tables and 1 figure.)