Parental monitoring, teacher support, classmate support, and friend relationship presumably affect adolescents' runaway from home. According to social control theory, social control based on conventional social norms would prevent adolescent runaway, but association with friends may erode such control. This expectation appears to hold true in a sample of Grade 7 students in Hong Kong; parental monitoring and classmate support reduced runaway risk whereas friend relationship raised the risk. These findings emerged from a causal model that controlled for a latent predisposition that commonly affected parental monitoring, friend relationship, and runaway risk. Further analysis indicates that the preventive effect of parental monitoring was stronger on adolescents born on the Chinese mainland than in Hong Kong, and the effect of friend relationship was stronger on the Hong Kong born than the mainland born. Conceivably, a socially controlling culture bolsters the preventive effect of social control.