Previous research has shown that parents underestimate their children's substance use. The aim of the present work was to analyze parental estimation of their children's use of alcohol in five countries from northern, central, and southern Europe, and to explore the variables that influenced this perceptual bias. The sample comprised 1181 parent-children dyads living in Sweden, Slovenia, the Czech Republic, Spain, and Portugal. In accordance with the findings of previous studies, we found high parental underestimation of substance use, which was greater for more frequent alcohol use or the use of illegal drugs. This underestimation appears to be subject to some degree of sociocultural influence, and is also influenced by the severity of the children's use.