Large, multiyear, state-managed clinical administrative databases provide important tools to inform decision makers about emerging trends in the nation's substance abuse treatment system. Such data can equip decision makers to monitor the responsiveness and efficiency of substance abuse treatment services and identify opportunities for improvement. This report presents an approach to conducting secondary analysis of state-managed clinical administrative and other management data on treatment episodes. It summarizes data on 54,049 clients from Colorado to assess trends in profiles of baseline admissions for clients' first encounters with Colorado's public treatment providers during the period of July 1991 and February 1999. Analyses include client profiles at admissions; treatment duration and completion; drug and alcohol use at treatment exit; and the likelihood that clients will return to treatment. The results revealed that overall success rates and interim drug use outcomes had not changed much in Colorado during the 1990s. About 75 percent had reduced substance use when they left treatment and about 10 percent were readmitted within a year. The report notes that the proportion of clients who were adolescent, female, and Hispanic increased, as well as the proportion of clients citing marijuana use. It suggests that in using this approach in the future, the characteristics and effects of contiguous and non-contiguous treatment admissions, the relationship of detoxification with other treatments, and combining information from other states should also be considered. (Contains 2 appendixes, 25 exhibits, and 35 references.) (JDM)