The report reviews the impact of prevalence estimation of drug use, AIDS, and crime on major policy development. The focus of the conference was to discuss common problems, identify useful information, and to constructively criticize estimation models presented. Topics discussed included measurement questions, new data sources in drug abuse estimation and further data improvements, Colorado social health survey using the synthetic model and the regression models, and the Epidemiologic Catchment Atea (ECA). New and improved statistical approaches to prevalence estimation examined were system dynamics, multiple capture and synthetic estimates, semi-Markov models, and the Burchmeyer-Gale procedure.