Adolescents with ASD often suffer from sleep disorders affecting their development and quality of life. Research concerning psychological treatment of insomnia in this population is scarce. The objective of this pilot study was to examine the feasibility of internet-delivered CBT for insomnia (iCBT-I) and the participants' experiences after completing the treatment. Both quantitative and qualitative methods were used. Six adolescents with ASD and insomnia, aged 13 to 17, participated in the study. The results of the qualitative investigation showed general satisfaction with the iCBT-I. The participants experienced both better sleep and insights into their sleep patterns. Thematic analysis revealed five themes: experience of the structure of the treatment, treatment content, experienced outcomes, experienced difficulties, and suggested improvements. The results indicate the need for additional support for some participants and suggest distinct recommendations for further studies. The quantitative investigation showed large reductions in insomnia symptoms indicating the feasibility of the treatment in this population. The findings suggest promising results, but more studies are needed to define the efficacy of iCBT-I for adolescents with ASD.