The CAHUS instrument included a comprehensive battery of questions that pertained to alcohol and other drug (AOD) use and treatment, general health, and mental health. The study used a probability sample that was stratified to obtain data for the following subpopulations: six State regions, two poverty levels, four age groups, and four ethnic groups. The CAHUS developed a sample of 5,555, and data were obtained by conducting a random digit dial telephone survey of households with telephones during the period between August 1995 and January 1996. The survey findings indicate that alcohol was the most widely used substance in all strata of the sample, with 75 percent reporting drinking in the past 12 months and 56 percent in the past 30 days. Marijuana was the next most frequently consumed drug, with 11.1 percent of respondents having consumed it within the past 12 months and 5.5 percent within the past 30 days. The use of other illicit drugs over the past 12 months was as follows: 1.9 percent for cocaine, 1.6 percent for amphetamines, 1.4 percent for hallucinogens, and 0.3 percent for opiates. Men's life time and past-12-month rates of substance use were higher than women's in all age, poverty-level, race/ethnic, and geographic group comparisons, except for the 18- to 24-year-old age group, in which no significant differences in opiate use were found between the sexes. An assessment of problem use in the past 12 months yielded two rates for adults in need of some type of intervention; using the stricter DSM-III-R definition of problem use, the rate of adults in need of some type of intervention was 4.8 percent; using the NTC (National Technical Center for Substance Abuse Needs Assessment) definition of problem use, 8 percent of the respondents required some type of intervention. Three percent of respondents reported ever having been in a formal alcohol or drug treatment program, and 6 percent reported having been in a 12-step program at some time in their lives. Study limitations are noted. 10 figures and 5 notes