The aim of this study was to assess key aspects of the reliability and validity of the "Modified Transplant Symptom Occurrence and Distress Scale," an instrument measuring symptom experience associated with side effects of triple drug therapy in transplant patients. This cross-sectional, comparative study included 108 renal transplant recipients (61% men; 39% women) with a median age of 47 years and a median posttransplant status of 5.5 years. Renal transplant patients were matched by age and gender with 108 healthy control persons not taking immunosuppressive drugs. Content validity, construct validity and discriminant validity of the instrument were substantiated. Internal consistency reliability was not useful to assess in this instrument, as the conditions for calculating Cronbach's alpha were not satisfied. These findings document the validity of the "Modified Transplant Symptom Occurrence and Symptom Distress Scale" as an instrument to measure symptom experience with immunosuppressive drugs.