The age of onset is one of the most important predictors of the development of risky and socially unacceptable behavior. It is the basis of the taxonomy that differentiates early and late starters. The aim of this research was to determine the contributions of different risk factors to socially unacceptable behavior in adolescent groups with different levels and ages of onsets of that behavior. Risk factors are riskiness of siblings, parents' behavior, internalizing problems, peer's characteristics (perception of their riskiness and peer influence) and academic achievement. This research included 661 male adolescents, high school students in third and fourth grades. They were divided into three groups: a group with a low level of the socially unacceptable behavior (N=227); a late-starter (N=231) and an early-starter group (N=203). The predictors are best in explaining the socially unacceptable behavior in the early-starter group. Internalizing problems, especially thinking problems, and peer's riskiness and peer influence were significant contributors. Contrary to previous studies, the perception of parental behavior contributed purely to the explaining of the socially unacceptable behavior. PUBLICATION ABSTRACT