Objectives. To examine the reliability and validity of spousal assessments by evaluating the collateral quality-of-life (QOL) ratings of patients of lower socioeconomic status with metastatic prostate cancer because collateral ratings provide supplemental information when advanced cancer limits patient self-report. Methods. Patients with Stage D2 prostate cancer (n = 36) of lower socioeconomic status completed validated QOL instruments (Functional Assessment of Cancer Therapy-General [FACT-G], European Organization for Research and Treatment of Cancer-Quality of Life-30, and Quality of Life Index). Spouses completed a modified FACT-G, and physicians rated performance status using Karnofsky's scale. Results. The internal consistency reliability was moderate to high for patient ratings on all FACT-G subscales and for spousal ratings on the modified FACT-G physical, functional, and emotional subscales. The spouses' ratings of the patients on the social and doctor relationship subscales were below the accepted criterion for a measure's use in group comparisons. The comparisons of the mean values of the FACT-G revealed agreement between patients and spouses, except that the spouses rated the patients as having poorer emotional function than did the patients. The intraclass correlations were moderate to high for the functional and emotional subscales and were low, but significant, for the physical and social subscales. The patient and spouse FACT-G ratings correlated with the patient ratings and physician ratings across the instruments for the functional and physical domains (r = 0.48 to 0.77, for patients; r = 0.31 to 0.70, for spouses), with less consistent relationships for the social and emotional domains. Conclusions. The collateral QOL assessments from spouses are potentially useful in assessing the functional status in patients of lower socioeconomic status with metastatic prostate cancer. For subjective domains, such as the social domain, direct patient assessments are needed. Copyright © 2001 Elsevier Science Inc.