The findings show that parents' knowledge of their emerging-adult child's activities varied as a function of parent reports and child reports. Child outcomes associated with parents' knowledge of their children's activities were generally positive, including less drinking of alcoholic beverages, drug use, and risky sexual behaviors, although the latter varied as a function of the reporter (parent or child). The links between maternal knowledge and lower drug and alcohol use were particularly strong in the presence of maternal closeness. The findings suggest that parents' interest in and involvement in their children's activities as a manifestation of parent-child closeness is a significant protective behavior against risky/problem behaviors during emerging adulthood. Study participants were drawn from a study of emerging adults and their parents entitled, "Project READY." The sample selected for the current study consisted of 200 undergraduate students (121 women and 78 men) and their fathers and mothers. Participants were recruited from four colleges across the United States. Parental knowledge was measured with Barber's Regulation Scale. Both emerging adults and their parents answered questions that assessed parent knowledge of children's activities and interests. Parental closeness with their children was measured with the Parent-Child Closeness Scale. Other instruments measured emerging adults' drinking of alcoholic beverages, drug use, and the number of sexual partners. 3 tables, 2 figures, and 48 references