Objectives: Sleep problems are prevalent among children with autism spectrum disorder (ASD) and are often accompanied by stereotypies, the function of which may be difficult to determine. Functional behavioral assessment (FBA) is an evidence-based approach to assessing and treating challenging behaviors, however, it has scarcely been used with sleep problems. This study investigates the effectiveness of FBA-based treatments for sleep disturbance (SD) in children with ASD, the short- and long-term maintenance of these effects, and parents' perspectives on the assessment and treatment process. Method: Two case studies used FBA to inform treatments for SD in two children with ASD and stereotypic behavior. The sleep-competing behaviors appeared to be multi-functional and included sleep interfering vocal stereotypy. The parents of each child implemented individualized, multi-component treatment packages. Results: Results demonstrate a reduction in SD for each participant, though delayed sleep onset latency remained for one participant. These results were maintained at short- and long-term follow-up. The interventions had high social validity. Conclusion: The implications of these findings for future research, and the assessment and treatment of SD in children with ASD and vocal stereotypy are discussed.