Research on family risk factors for addictive behaviors in young people has not paid a great deal of attention to parents' knowledge of their children's addictive behaviors and of the family risk factors that affect such behaviors. The aim of this work is to compare knowledge about these two aspects in two groups of parents that differ regarding their children's declared drug use. The research was carried out with a sample of 309 schoolchildren and their families, divided into two groups: one of 154 families with children defined as non-Drug Users and another of 155 families with children defined as Drug Users. The results show that parents with children who consume drugs tend to strongly underestimate their children's use. Moreover, they overestimate the control they exercise over them and appear to be more familiarized with the use of drugs, if we compare them with parents of non-Drug Users. It is suggested that these results may be relevant for the planning of strategies that increase motivation in families with drug-risk children to participate in prevention programs. (Contains 3 tables.)