To assess current documentation of treatment-related toxicity, 46 out-patients attending the Ottawa Civic Hospital Cancer Clinic were randomly selected. Physician's charting of toxicities was compared to patient's perception of toxicity, as recorded on a brief questionnaire. As a group, patients reported significantly more toxicities than had been recorded by their physician. The greatest disparity was observed for the following categories: nausea, vomiting, alopecia, and decreased performance status. The best-documented toxicities were: skin and mucosal reactions, and urinary symptoms. To the question concerning their most bothersome symptoms, patients described nausea, vomiting, mucosal reaction, and decreased performance status as the most common. In 46% of cases, the physician's notes failed to identify the patient's worst symptom. From our study; toxicity is probably under-reported, and unrecognized by oncologists. A self-administered questionnaire appears to be a better way of accurately identifying and reporting treatment toxicities, when compared to the oncologist's evaluation, as recorded in the patient's permanent record.