Defining illegal drug use expenditures as monies spent on illegal drugs and legal drugs that are used illegally, the Office of National Drug Control Policy presents this biennial report on illegal use expenditures. The data for the report cover 1998 and 1999 with estimates for 2000. As compared to earlier reports, this report does not include drug supply flow analysis or price estimate derivation description, but a prevalence-based procedure was used to derive cost estimates. Information is presented for the specific drug types that account for the majority of expenditures. These drugs include cocaine, heroin, methamphetamine, and marijuana. Limited analysis and statistical data for "other drugs" which include inhalants, hallucinogens, and the illicit use of otherwise legal substances are also provided. In general, the authors found that the total illegal drug use expenditure was $67 million in 1999, but that these expenditures had substantially decreased since 1990. 11 tables, 53 notes, appendix