Adolescence is challenging time for youth with autism spectrum disorder (ASD), who generally exhibit a myriad of psychosocial difficulties. While this developmental period represents an important window for intervention, few evidence-based programs exist. Recent research suggests that interventions targeting emotion regulation (ER) skill deficits in ASD may represent a promising approach to promoting more favourable outcomes for these youth (Mazefsky et al., 2014). Nurturing mindfulness has been shown to be an effective means of improving ER and wellbeing in diverse child and adult populations, although research in ASD is limited. This pilot study evaluated the impact of a 9-week mindfulness intervention on the ER and socioemotional functioning of 14 adolescents (13-17 years) with high functioning ASD using a pre-test post-test design. Parents reported statistically significant changes of small to medium effect size in adolescents’ overall problem behaviours and social skills, ER, adaptability, hyperactivity, and withdrawal behaviours. Additionally, parents reported changes of small effect size that approached significance for adolescents’ anxiety symptoms and atypicality. Adolescents reported changes of small effect size that were statistically significant for anxiety symptoms and interpersonal functioning, and non-significant for depression and social stress symptoms. Changes in many parent-reported outcome variables showed moderate to strong correlations with home practice adherence and parent-reported changes in ER. Qualitative observations of program impact and social acceptability were positive and supported the quantitative findings. The results provide promising evidence for mindfulness training with youth with ASD. Implications for assessment, intervention, and future research are discussed. / October 2016