Systematic assessment of pain is the basis for adequate pain treatment. In the home situation, however, it is difficult to assess patients' pain intensity. A group of 159 cancer patients who had been admitted to a cancer hospital with pain caused by cancer, cancer therapy, or illness that persisted for at least 1 month received a pain diary. These patients were asked to register their pain intensity at home. Patients were instructed by a nurse to record their Present Pain Intensity on a scale from 0-10 once every morning and every evening for a period of 2 months. In this study, the use of a pain diary in cancer pain patients at home was evaluated. To determine the effects of the pain diary, patients were interviewed at baseline, at 2, 4, and 8 weeks postdischarge. Pain intensity scores were obtained both by patient interviews and from the pain diary. Results show that the use of a pain diary is an appropriate way to assess patients' pain intensity at home. Patients' compliance was high (86%), even in seriously ill patients. When comparing pain scores obtained by patient interview with scores obtained by pain diary, results showed that Present Pain Intensity scores, rather than Average Pain Intensity scores, should be used in both the clinical and the home setting because patients' recall accuracy depends, in part, on the stability of the pain. Because the pain intensity scores fluctuate greatly during the day and over a period of time, the use of a pain diary is useful in the home setting. In 60% of the patients, completing the pain scores helped them to cope with the pain.