This paper presents principles that should be considered in planning and interpreting studies of outcomes of interventions with children receiving mental health services. Principles to consider when planning outcome studies include recognizing that "outcome" refers to multiple rather than single domains and choosing outcome domains that coincide with program theory. Principles to consider when interpreting results of outcomes studies include the following: (1) consider the source of information when evaluating outcome results; (2) recognize that clinical outcomes are not solely the result of services; (3) evaluate for adequate statistical power and appropriate procedures in data analysis; and (4) remember that conclusions are limited by the chosen outcome domains. (DB)