While parental knowledge of adolescents’ whereabouts is generally considered to be a key protective factor for adolescent alcohol use, the developmental links during adolescence are unclear. Focusing on within-family processes on a sample of Swedish early to late adolescents (n = 782; 49% female) over four waves of data, we (1) tested the interplay between parental knowledge and adolescent alcohol inebriation, (2) investigated whether changes over time in parental knowledge and adolescent inebriation were linked to the parent–child relationship, and (3) tested the moderating role of adolescent gender and SES on these potential links. The results from random intercept cross-lagged panel models showed that increases in parental knowledge predicted decreases in frequencies of adolescent inebriation the following year as well a more positive parent–child relationship over time. Increases in adolescent inebriation were predicted by less parental knowledge only in late adolescence. These links were not moderated by adolescent gender or SES. The results emphasize the importance of increasing parental knowledge of adolescent activities in order to reduce adolescent involvement in heavy alcohol use as well as the importance of parent–child closeness.