This study presents information on the test-retest reliability of the Health Utility Index--Mark III (HUI) system used in cycle 6 of the Canadian General Social Survey (GSS). The HUI system used in this reliability study consists of an eight-attribute health status classification system (HSCS) and a function for generating a summary score of health-related quality of life. To estimate test-retest reliability, a stratified random sample of individuals (n = 506) completing GSS telephone interviews during August and September, 1991 were interviewed again 1 month later. Weighting adjustments based on the probability of selection were invoked during the analyses to provide unbiased estimates of test-retest reliability for all GSS respondents in the August-September period. The results indicate that the individual questions, attributes and provisional index scores generally provided reliable information on health status in the GSS. The exceptions to this were limitations in speech and dexterity which were reported very infrequently. Kappa estimates of test-retest reliability for individual questions varied from 0.184 to 0.766. For the eight attributes, kappa estimates varied from 0.137 to 0.728. Using the provisional index scores to quantify health overall, a test-retest reliability of 0.767 was obtained (intra-class correlation coefficient).