Background: Despite the dramatic increase in autism spectrum disorder in youth and the extremely high costs, hardly any evidence-based interventions are available. The aim of this study is to examine the effects of mindfulness training for adolescents with autism spectrum disorder, combined with Mindful Parenting training. Method: A total of 23 adolescents with autism spectrum disorder, referred to a mental health clinic, received nine weekly sessions of mindfulness training in group format. Their parents (18 mothers, 11 fathers) participated in parallel Mindful Parenting training. A pre-test, post-test, and 9-week follow-up design was used. Data were analyzed using multi-level analyses. Results: Attendance rate was 88% for adolescents and fathers and 86% for mothers. Adolescents reported an increase in quality of life and a decrease in rumination, but no changes in worry, autism spectrum disorder core symptoms, or mindful awareness. Although parents reported no change in adolescent's autism spectrum disorder core symptoms, they reported improved social responsiveness, social communication, social cognition, preoccupations, and social motivation. About themselves, parents reported improvement in general as well as in parental mindfulness. They reported improved competence in parenting, overall parenting styles, more specifically a less lax, verbose parenting style, and an increased quality of life. Discussion: Mindfulness training for adolescents with autism spectrum disorder combined with Mindful Parenting is feasible. Although the sample size was small and no control group was included, the first outcomes of this innovative training are positive.