The cohort for the study was the sentenced population of the correctional institution as of June 21, 1978. Various types of substance abuse were cross-tabulated with age, most serious current offense, length of sentence, previous criminal record, and previous incarcerations at the youth training school. Substance abusers were divided into three categories: alcohol abusers, marijuana abusers, and abusers of other drugs (such as opiates, hallucinogens, etc.). Data analysis reveals that 81 percent of the sentenced population had abused at least one substance. Slightly more than 40 percent had abused alcohol, and 38.5 percent had used marijuana. Well over 50 percent of the inmates had abused at least one substace other than alcohol or marijuana. The most widely abused substance was alcohol, followed by marijuana, opiates, and downers. Alcohol abuse was most common at ages 35 through 39, marijuana abuse was highest at ages 18 to 19, and opiate use was most common at ages 25 through 29. The proportion of substance abusers was slightly higher among white inmates than among blacks or Hispanics. Alcohol abuse was more prevalent among whites, and opiate use was more common among Hispanics.All 38 inmates whose most serious offense was a drug charge were substance abusers. This group was less likely to abuse alcohol than the prison population at large but was more likely to have abused every other type of substance. Extensive statistical tables are provided.