Prolonged waiting times to receive mental health services are common and may have negative consequences. This study examines the relationship between waiting time and treatment engagement among 2,054 youth referred to an evidence based treatment (EBT). Findings indicate that families are more likely to refuse services if they face longer waiting times. Families exposed to a prolonged waiting time were also more likely to drop out prematurely from Functional Family Therapy, but this relationship was not significant among youth receiving Multisystemic Therapy. Implications for EBT implementation and strategies for engaging families are discussed.