Missed appointments are detrimental to the healthcare system and to the clients themselves. Autistic youth may be particularly impacted due to unique service needs and limited services available within the system. To date, there is limited literature specific to treatment attendance in autistic populations receiving behavioral services. This study examines prevalence, predictors of, and reasons for missed appointments in an outpatient clinic specializing in addressing behavioral concerns. This retrospective case review examines missed appointments in a sample of 306 autistic youths from an outpatient clinic from 2019 to 2022. An average of 5.2 appointments were cancelled and 9.0 were completed, resulting in an average individual cancellation rate of 38%. Statistically significant predictors of no shows and patient cancellations were younger age and a post-COVID appointment. The most common reasons for missed appointments was sickness, scheduling conflict, insurance authorization issues, and family emergency. Missed appointments may be common in outpatient behavioral settings for autistic youth. Resolving issues related to cancellations (e.g., sleep concerns), identifying families in need of targeted support strategies (e.g., assistance and flexibility with scheduling, transportation support), and advocating for systemic change may help meet the multifaceted needs of this population.