The purpose of this study was to examine the utility of the Personal Experience Inventory (PEI) as a measure of change in adolescent drug misuse. One year test-retest reliability of the PEI Problem Severity Scales was measured in a sample of drug-misusing adolescents who did not receive treatment during the 1-year test-retest interval (n = 37). The five PEI Problem Severity Scales demonstrated satisfactory 1 year temporal stability coefficients, ranging from .86 to .89. The utility of the PEI as a measure of change was demonstrated by using the 1-year test-retest reliability data to measure both statistically significant and clinically significant change between admission and 1-year follow up in a sample of drug-misusing adolescents who received treatment (n = 45). The PEI was useful in identifying which treatment clients exhibited statistically significant improvement, statistically significant deterioration, and no reliable change.