Background <p>Individuals with eating disorders (EDs) often exhibit impairments in executive functioning, including nonverbal reasoning. However, little is known about how nonverbal reasoning interacts with illness duration, influences ED symptom changes over time, or differentially affects phenotypically distinct EDs. This study examined associations among nonverbal reasoning, illness duration, and changes in ED symptoms in individuals with anorexia nervosa (AN) and bulimia nervosa (BN).</p> Methods <p>Adults with AN or BN (<i>N</i> = 83; mean age = 25.9) completed baseline assessments of ED symptoms, illness duration, nonverbal reasoning, height, weight, and anxiety and depressive symptoms. ED symptoms and weight were reassessed at 3 and 6 months after baseline. Linear regression analysis and multilevel modeling were used to evaluate associations between nonverbal reasoning, illness duration, and ED symptom trajectories.</p> Results <p>In the AN group, longer illness duration was significantly associated with poorer baseline nonverbal reasoning, even after adjusting for BMI. There was no significant association between illness duration and nonverbal reasoning in the BN group. Among individuals with BN, better baseline nonverbal reasoning predicted a greater reduction in ED symptoms over 6 months, while poorer baseline nonverbal reasoning was associated with no significant change in symptoms. In AN, nonverbal reasoning did not predict ED symptom change from baseline to follow-up.</p> Conclusions <p>In AN, longer illness duration was linked to poorer nonverbal reasoning, whereas in BN, better nonverbal reasoning predicted improvement in symptoms over time. These findings support the relevance of nonverbal reasoning to AN and BN. Future longitudinal studies are needed to confirm the findings and gain additional insights into associations among nonverbal reasoning, illness duration, and ED symptoms.</p>