Although theories suggest transactional associations between adolescents’ autonomy and relationships with parents and friends, few studies have examined these within-person effects. This longitudinal study examined the within-person co-development of adolescents’ autonomy and relationships with parents and friends. Adolescents (N = 244 M
age = 11.54, SD = 0.43 at T1; 50% boys) participated in a four-wave study across 2 years in the Netherlands. In random-intercept cross-lagged panel models, within-person results showed that higher levels of autonomy predicted less parental psychological control but not vice versa. However, no lagged-effects between friend support and autonomy were found. This study suggests that adolescents’ autonomy steers changes in parental psychological control.