This study examined the usefulness of caregiver ratings of cancer patients' quality of life (QOL), an issue of relevance to both adequate patient care and to the possible use of proxy QOL raters in clinical studies. We compared QOL ratings of 90 cancer patients receiving inpatient chemotherapy with those provided by their significant others (most often the spouse), physicians and nurses. During patients' scheduled appointment for receiving chemotherapy on a clinical ward, all raters completed independently the Dartmouth COOP Functional Health Assessment charts/WONCA, an instrument developed by a cooperative group of primary care physicians to briefly assess a core set of seven QOL domains (physical fitness, feelings, daily and social activities, overall health, pain and quality of life) by single items with five response options. With few exceptions, mean scores of the proxy raters were equivalent or similar to those of the patients. Most patient-proxy correlations varied between 0.40 and 0.60, indicating a moderate level of agreement at the individual level. Of all comparisons made, 41% were in exact agreement and 43% agreed within one response category, leaving 17% more profound patient-proxy discrepancies. Disagreement was not dependent on the type of proxy rater, or on raters' background characteristics, but was influenced by the QOL dimension under consideration and the clinical status of the patient. Better patient-proxy agreement was observed for more concrete questions (daily activities, pain) and for patients with either a very good (ECOG 0) or poor (ECOG 3) performance status. The results indicate that both significant others and health care providers can be useful sources of information about cancer patients' QOL.