Autistic adults are at risk of stress-related psychiatric disorders and reduced life quality due to social, cognitive, and perceptual challenges. Mental health interventions adapted to autistic adults are scarce. Acceptance and commitment therapy has preliminarily indicated health benefits in autistic adults, although it has not been robustly evaluated. Overall, 39 adults (21 males; 21-72 years) with autism spectrum disorder and normal intellectual ability (IQ M = 108.5; SD = 13.5) were randomized to 14 weeks of adapted acceptance and commitment therapy group treatment (NeuroACT) or treatment as usual. The intervention was feasible. Perceived stress and quality of life (primary outcomes), alongside psychological inflexibility, cognitive fusion, cognitive and behavioral avoidance, and autistic mannerism were statistically significantly improved in NeuroACT compared with treatment as usual (d = 0.70-0.90). Clinically significant changes in perceived stress and quality of life were in favor of NeuroACT. Between-group altered depression, anxiety, sleep problems, one quality of life measure, functional impairment, social aspects of autism, and executive difficulties were statistically non-significant. Dropout was slightly higher in NeuroACT. NeuroACT may be a promising treatment for autistic adults with co-existing stress and reduced quality of life. More extensive studies are warranted to evaluate NeuroACT further.