Most studies that explore parental knowledge of youths' activities utilize parents' and youths' reports separately. Using a sample of 938 rural early adolescents (53% female; 84% White), we explore congruence between mothers' and youths' perceptions of maternal knowledge and its association with youth problem behaviors (delinquency, substance use, and attitudes towards substances). Maternal overestimation of knowledge (compared to youths' ratings) was positively associated with delinquency and negatively associated with healthy drug attitudes. Significant differences in problem behaviors were found between four groups created based on mothers' and youths' level of knowledge (High Youth and Mother, High Youth/Low Mother, Low Youth/High Mother, and Low Youth and Mother). The High Youth and Mother group demonstrated less substance use and healthier drug attitudes than the Low Youth and Mother group. The Low Youth/High Mother group had significantly higher levels of substance use and delinquency than the High Youth and Mother group. Intervention implications are discussed.