Evidence suggests that youth with autism spectrum disorder (ASD) are at increased risk for experiencing a mental health crisis. Yet, limited systematic research exists on this topic. This study examines the prevalence, phenomenology, and correlates of mental health crisis in children, adolescents, and young adults with ASD. Participants included 462 parents of individuals with ASD (83% male, 86% Caucasian, M = 13.7 years, SD = 4.7) who were enrolled in the Interactive Autism Network, a large online registry of families of individuals with ASD. Parents completed the Mental Health Crisis Assessment Scale, a psychometrically sound measure of mental health crisis for youth with ASD, as well as measures of parental depression, family quality of life, and mental health treatment history. Overall, 32% of parents reported that their child had experienced a mental health crisis during the last 3 months. In the younger group, elopement (88%) and self-injury (81%) were the most frequent behaviors contributing to crisis; physical (60%) and verbal (42%) aggression were the most frequent crisis behaviors in the older group. Correlates of crisis included younger age, increased parental depressive symptoms, and lower family quality of life. Approximately 75% of individuals in crisis had seen a psychiatrist or behavioral therapist/psychologist within the last 3 months and 25% were not engaged in any mental health treatment. In summary, mental health crises were quite prevalent in this online sample of youth with ASD. Identiﬁcation and treatment of these serious events is critical to reduce morbidity in this population.