This Dutch multi-informant study examined effects of the first COVID-19 lockdown (e.g., school closure and social restrictions) on parent-adolescent relationships. Four bi-weekly measurements before and four bi-weekly measurements during the lockdown were collected among adolescents (N = 179, Mage = 14.26 years, 69% girls) and their parents (N = 144, Mage = 47.01 years, 81% female). Parents’ educational level was relatively diverse; 12% low (high school or lower), 33% medium (vocational training), 55% high (college or university). Adolescents and parents reported on parental support, parent-adolescent conflict, autonomy support, psychological control, behavioral control, and time spent on various activities. Adolescents spent more time with their parents during lockdown (before M = 8.6h, during M = 12.7h), but less time with friends (before M = 8.1h, during M = 2.1h), and reported on average 13 COVID-19-related rules. Pre-registered piece-wise growth models confirmed that autonomy support decreased immediately during the lockdown, but no mean level changes were observed in the other relationship dimensions. During the first two months of the lockdown, parents reported gradual increases in autonomy support and decreases in behavioral control. Moreover, significant differences between families were found in sudden and more gradual relationship changes, which correlated strongly with pre-lockdown characteristics of the relationship, and in some models with adolescent oppositional defiance and legitimacy beliefs. In sum, findings suggest resilience in most families, but also heterogeneity; Some families were negatively affected and others were positively affected. A tailored approach is therefore needed to mitigate the impact of COVID-19 on family functioning.