Utilizing primary socialization theory (PST) and longitudinal survey data from 381 Latina/o sixth- through eighth-grade students, we hypothesized that four types of parent anti-substance use messages (i.e., parents' own past substance use, religious beliefs, respect for family, and peer resistance) would discourage Latina/o students' substance use, particularly when the students perceived their parents' anti-substance use messages were legitimate. The results supported moderation. For Latina/o students who thought that their parents' anti-substance use messages were legitimate, many of the anti-substance use messages were negatively related to substance use, but the associations were positive or nonsignificant for Latina/o students who thought that their parents' anti-substance use messages were not legitimate. The findings extend past work on PST and anti-substance use parent-child communication, highlighting the importance of perceived legitimacy and message content.