Psychological resources were investigated in 150 recently diagnosed adult cancer patients and in 150 healthy control group members. Before the start of chemotherapy, cancer patients reported higher levels of optimism, purpose in life than their healthy peers, and self-esteem (only younger patients) whereas no between-group differences emerged for internal locus of control. However, the mobilization of psychological resources was limited to younger patients, and varied by item content. Over a 9-month period, most psychological resources of cancer patients showed a small but significant decline, and patients with higher illness-related stressors (e.g. stronger functional impairments, low perceived success of therapy) were more likely to decline in resources. We conclude that in line with cognitive adaptation theory cancer diagnosis leads to an initial mobilization of psychological resources in younger patients, but that over the course of therapy psychological resources decline to a level that would be expected in healthy adults. Copyright © 2006 John Wiley & Sons, Ltd.