Opiate addicts living with family members generally have better treatment outcomes than addicts who live alone, but family support for the addict remaining drug-free depends on the family being aware of the addiction. We found that many addicts deny their drug abuse to their families and we hypothesized that these addicts would have poor treatment outcomes, even though they lived with nonaddict family members. To test this hypothesis, four groups of addicts in a naltrexone program were compared: 28 male addicts with their spouses, 27 addicts living with their parents, 23 addicts who denied their drug abuse to the family members with whom they lived, and 28 addicts who lived alone. The first two groups participated in family therapy, and these addicts remained drug-free longer than the other two addict groups (analysis of variance, p less than 0.001). The addicts who denied their drug abuse to their families remained drug-free for significantly less time than those who admitted their drug abuse to their families. Furthermore, addicts who admitted their drug abuse to their spouse, but denied it to their parents, remained drug-free for shorter times than married addicts who also told their parents. Thus, maximum family involvement in treatment including spouses and parents was associated with a better prognosis.