At-risk behaviour is a set of presumed cause and effect dynamics that place the adolescent in danger of negative future events. It not only endangers the life of the person involved but also the lives of others around. Considering the urgent need to prevent adolescents from engaging in at-risk behaviours, this study investigated parenting styles as correlates of at-risk behaviour among in-school adolescents in Nigeria. The descriptive survey of the correlation type was adopted for the study. The target population was all in-school adolescents in Nigeria. One thousand two hundred (1,200) in-school adolescents were selected for the study from three geo-political zones in Nigeria, using the multistage random sampling procedure. The instrument used consists of questions on at-risk behaviour scale and the parenting style scale. The findings revealed that more male than female in-school adolescents in Nigeria were involved in at-risk behaviours. The at-risk behaviour associated with anger ranked 1st among the four at-risk behaviours. It is therefore recommended that the government should ensure that all secondary schools (both private and public owned) have professional counsellors to assist in handling challenges ameliorating anger, sexual, substance, and cultism among in-school adolescents in Nigeria