Introduction: Lie-telling appears to peak during adolescence; however, previous research has not yet examined lie-telling frequency in adolescents' friendships. Increased lie-telling may be problematic given that honesty is crucial for trust within positive relationships, and more positive relationships lead to more positive well-being. The present study examined adolescents' lies to friends and longitudinal associations between lying, friendship quality, and depressive symptoms. Methods: Canadian adolescents (Time 1: N = 1313, M age = 11.65, SD = 11.75, 50% male) reported how often they lied to their friends about their mental health/mood, possessions, romantic relationships, school, and to avoid spending time with them. Participants also completed measures of friendship quality and depressive symptoms. Participants completed these measures at two time points one year apart. Results: Poorer friendship quality predicted more frequent lie-telling over time. Greater depressive symptoms predicted more frequent lie-telling over time, and more frequent lie-telling predicted greater depressive symptoms over time. Lies about mental health in particular were bidirectionally associated with both friendship quality and depressive symptoms over time. Conclusions: These indings highlight the developmental importance of lie-telling during adolescence. More negative friendships lead to greater lie-telling over time. Additionally, increased lietelling predicted and is predicted by depressive symptoms, suggesting that lie-telling may be an important indicator of poor mental health.Building positive friendships is an important aspect of adolescence, a task for which building trust is vital. One of the key features of trust is honesty (Rotenberg, 1994), such that dishonesty can violate trust while honesty can strengthen trust. Yet, adolescents report telling lies more frequently than any other age group (Debey, De Schryver, Logan, Suchotzki, & Verschuere, 2015; Levine, Serota, Carey, & Messer, 2013). Given that lie-telling violates the expectation of honesty in interpersonal relationships, increased lie-telling during adolescence may be detrimental to the development of positive friendships. Additionally, if adolescents engage in behaviors that disrupt their friendships, such as lie-telling, they may prevent their friendships from becoming forms of support that protect against negative experiences like depression. Thus, the present study examined the associations between lie-telling frequency, relationship quality, and depressive symptoms over time during late childhood and adolescence.Lie-telling, the act of stating information one believes to be false but intends for another to believe to be true, emerges in the