Confirmatory factor analysis was used to test the structure of 5-item affect rating scales designed to measure positive affect and negative affect. A proposed circumplex affect structure was the source of scales constructed to represent a cluster of positive terms, including pleasantness and activation; the negative terms represented anxiety, depression, and hostility. The hypothesized simple-structured positive and negative trait affect factors, with a moderate correlation between them, were found in all cases. Equivalent structure was confirmed for younger adults, middle-aged, and older adults of good health and above-average education. Although the hypothesized simple-structured positive and negative factors emerged for all other groups, three other tests of factor equivalence failed to be confirmed: trait and state factors in the older adult group were not identical. Factors derived from healthy and frail elders were structurally different. Variability among frail elders and variability over 30 days within the same person, when factored, also showed nonequivalence. Although the scales are extremely useful in assessing affect, comparisons across some subject groups should be made with caution.