The aim of this study was the development and psychometric testing of a new psychological questionnaire to measure the fear of progression (FoP) in chronically ill patients (cancer, diabetes mellitus and rheumatic diseases).The Fear of Progression Questionnaire (FoP-Q) was developed in four phases: (1) generation of items (65 interviews); (2) reduction of items--the initial version of the questionnaire (87 items) was presented to 411 patients, to construct subscales and test the reliability; (3) testing the convergent and discriminative validity of the reduced test version (43 items) within a new sample (n=439); (4) translation--German to English.The scale comprised five factors (Cronbach's alpha >.70): affective reactions (13 items), partnership/family (7), occupation (7), loss of autonomy (7) and coping with anxiety (9). The test-retest reliability coefficients varied between .77 and .94. There was only a medium relationship to traditional anxiety scales. This is an indication of the independence of the FoP. Significant relationships between the FoP-Q and the patient's illness behaviour indicate discriminative validity.The FoP-Q is a new and unique questionnaire developed for the chronically ill. A major problem and source of stress for this patient group has been measuring both specifically and economically the FoP of an illness. The FoP-Q was designed to resolve this problem, fulfill this need and reduce this stress.