The literature on chronic diseases recognizes the role of illness cognition as a mediator between stress and illness. Few conceptualizations and instruments, however, give an indication of both unfavorable and favorable ways of adjusting to an uncontrollable long-term stressor, such as a chronic disease. The authors propose 3 generic illness cognitions that reflect different ways of reevaluating the inherently aversive character of a chronic condition: helplessness as a way of emphasizing the aversive meaning of the disease, acceptance as a way to diminish the aversive meaning, and perceived benefits as a way of adding a positive meaning to the disease. A self-report instrument, the Illness Cognition Questionnaire, was developed to assess these cognitions across different chronic diseases. The results support the reliable and valid assessment of these illness cognitions in patients with rheumatoid arthritis and multiple sclerosis and indicate the maladaptive function of helplessness and the adaptive function of acceptance and perceived benefits for the long-term physical and psychological health of patients with a chronic disease.