Outcomes for autistic adults are generally poor across multiple foundational metrics, including activities of daily living and quality of life. Co-occurring psychiatric conditions contribute to these poor outcomes. Attention-deficit/hyperactivity disorder is one of the most common co-occurring conditions among autistic individuals; however, we know little about the association of attention-deficit/hyperactivity disorder symptoms with autistic adult outcomes. A total of 724 autistic adults (18-83 years; 58% female) recruited via Simons Foundation Powering Autism Research (SPARK) Research Match completed questionnaires on demographics, co-occurring attention-deficit/hyperactivity disorder symptoms, activities of daily living, and subjective quality of life. After controlling for age, birth-sex, socioeconomic status, and autistic traits, attention-deficit/hyperactivity disorder symptoms explained an additional 2%-10% of variance across activities of daily living and all domains of subjective quality of life. This is the first study to demonstrate that autistic adults who rated themselves as having more attention-deficit/hyperactivity disorder symptoms also rated themselves as less independent in activities of daily living and experiencing a lower subjective quality of life. These findings highlight that additional research and better supports for co-occurring attention-deficit/hyperactivity disorder symptoms may be critical to enhancing independence and quality of life for autistic adults.