The cognitive style of rumination extends existing cognitive models of emotional response to illness. In the absence of a specific measure, we developed the Multidimensional Rumination in Illness Scale (MRIS). In Study 1, an initial 60-item pool was tested, followed by confirmation of the factor structure in Study 2. In Study 1 participants (n = 185) completed the pilot version of the MRIS, then in Study 2 (n = 163) a reduced 41-item model was tested. Study 1: Exploratory factor analysis of a reduced 32-item scale indicated an initial four-factor solution for the MRIS (Intrusion, Brooding, Instrumental, Preventability), with satisfactory internal consistency and stable factor structure across gender. Study 2: Following scale revision, confirmatory factor analysis substantiated the adequacy of a three-factor MRIS structure, and good internal consistency, test-rest reliability, and concurrent and discriminant validity was demonstrated for the MRIS. The MRIS exhibited good psychometric properties in the current sample, providing a comprehensive assessment of the cognitive style of rumination in the context of physical illness.