Inflammatory bowel disease (IBD), encompassing both Crohn's disease and ulcerative colitis, is characterized by unpredictable symptoms that potentially lead to uncertainty in patients. This study of 42 IBD patients was undertaken to: (1) examine selected components of Mishel's Theory of Uncertainty in illness, (2) compare the psychological and symptom experience of IBD patients in exacerbation with those in remission, and (3) describe patterns of symptoms over a 4-week period. Uncertainty was positively related to number of symptoms and psychological distress and negatively related to social support at week 1 (T1) and week 4 (T4). At T1, 48% of the variance in uncertainty was explained by education, symptoms and social support; at T4, 23.8% was explained by the model. Patients experiencing exacerbations had higher levels of uncertainty, symptoms and psychological distress at T1 and T4, and lower levels of social support at T1 than did those in remission. Significant differences in symptom levels occurred over time with symptoms decreasing from T1 through T3, then increasing. However, there was an interaction between time and exacerbation/remission status, such that patients in exacerbation experienced more marked changes in symptoms than those in remission. Social support decreased between T1 and T4, but levels of psychological distress and uncertainty did not change. Implications for nursing care of IBD patients were suggested.