This study investigated a patient's ego strength (Es) at the time of an initial cancer diagnosis and its relationship, over time, to mood disturbance, vulnerability, self-reported physical symptom totals, current concerns, coping strategies, and effectiveness in the resolution of problems. The subjects were 163 newly diagnosed male and female cancer patients representing five primary tumor sites. All patients were seen for an initial evaluation, at which time they completed Barron's Es scale, the Profile of Mood States, the Inventory of Current Concerns, and a semistructured interview. Ratings on patient vulnerability, coping strategies, and problem resolutions were made at each of the five follow-ups. Results showed that psychosocial adaptation to cancer was related to a patient's ego strength. Es correlated positively with a patient's use of effective coping strategies. The concept of Es and problems with Es assessment were discussed within a cognitive-ego analytic frame of reference.