Background <p>Families of adolescents with severe behavior problems and an Autism Spectrum Disorder (ASD) level 1 may experience a variety of problems in their functioning. Research suggests that these problems across multiple life areas are best treated with intensive, flexible, and home-based treatment such as Multisystemic Therapy (MST). However, little is known about the treatment results of MST for families of autistic adolescents. OBJECTIVE: In two Single Case Experimental Design (SCED) studies (<i>N</i> = 14 families), the treatment outcomes and effects of MST were assessed.</p> Methods <p>An observational AB study design was employed. Families receiving treatment as part of two cohorts were asked to participate in the two studies.</p> Results <p>Overall, some positive changes were observed during MST treatment. Of 22 parents, 8 parents showed significant improvement based on the Reliable Change Index. Tau-U analyses used in both studies reveal that there was little evidence of treatment effect, despite families reporting positive experiences with treatment during interviews. A meta-analysis of Tau-U scores revealed no overall effect for the total study population and a small effect for mothers.</p> Conclusions <p>Little treatment effect was observed in these SCED studies. <i>When</i> changes or effects were observed following MST treatment, these tended to be positive. To reach firmer conclusions, a larger and more robust study would be needed. More research is also needed to attain a better understanding of how to best support families of young autistic people.</p>