Data from a longitudinal study of 250 older adults were used to examine activity loss and replacement as a consequence of an important illness episode. Multiple regression analyses revealed that reductions in activity were predicted by physical factors, specifically illness chronicity and severity. In contrast, replacing lost activities was facilitated by social support and optimism and inhibited by a belief in the need to conserve physical resources. An examination of the long-term benefits of replacing activities revealed that older adults who replaced a lost activity had higher positive affect levels 1 year after illness onset than those who did not replace activities. Continuing activity during illness episodes can help maintain positive well-being over time.