The relationship of diabetic patients' psychosocial adjustment to disease type, treatment mode, and indexes of control was examined in a representative community population. The psychometric properties of the Diabetes Educational Profile (DEP) and its application to psychosocial research in diabetes were also investigated. Findings support the reliability and validity of the DEP. Various measures of psychosocial adjustment were related to diabetes control but the specific relationships depended on the particular aspect of adjustment, the specific measure of diabetes control, and the type of disease and treatment. The findings suggest that analyses that aggregate dissimilar patient groups are subject to misinterpretation due to ecological masking and supressor effects. The results indicate that clinicians and researchers must recognize that patients with different disease types and treatment modes have different norms for psychological adjustment and diabetes control. Further, the particular aspects of psychosocial adjustment associated with diabetes control differ across patient groups.