The present cross-sectional study analyzed the extent to which illness perceptions and coping strategies (as measured by the Illness Perception Questionnaire and the Utrecht Coping List, respectively) are associated with levels of daily functioning, as indicated by the Medical Outcomes Study SF-20, and disease-specific measures in 244 adults: 84 with rheumatoid arthritis (RA); 80 with chronic obstructive lung disease (COPD); and 80 with psoriasis. The results of stepwise regression analyses indicated that a strong illness identity, passive coping, belief in a long illness duration, belief in more severe consequences, and an unfavorable score on medical variables were associated with worse outcome on disease-specific measures of functioning and on general role and social functioning. Coping by seeking social support and beliefs in controllability/curability of the disease were significantly related to better functioning. The implications of these findings for future interventions and research are discussed.