AbstractObjectiveNo prior studies have evaluated inhibitory control in people with severe class III compared with class I/II obesity. Thus, the study aim was to evaluate inhibitory control and neural correlates of response inhibition by obesity class using a sample of endometrial cancer (EC) survivors with obesity, who have a higher risk of overall but not cancer‐specific mortality.MethodsForty‐eight stage I EC survivors with obesity (class I/II: n = 21; class III: n = 27) seeking weight loss in a lifestyle intervention at baseline completed a stop signal task during functional magnetic resonance imaging.ResultsIt was found that participants with class III obesity had a longer stop signal reaction time (mean [SD], 278.8 [51.3] vs. 251.5 [34.0] milliseconds, p < 0.01) compared with those with class I/II obesity, indicating that patients with EC with severe obesity had greater impulsivity and poorer inhibitory control. Results also showed increased activation in the thalamus and superior frontal gyrus for the incorrect versus correct inhibition contrast in class III but not class I/II obesity (whole brain cluster corrected, p < 0.05).ConclusionsThese results provide novel insights into inhibitory control and corresponding neural correlates in severe versus less severe classes of obesity and highlight the importance of targeting inhibitory control processes in weight‐loss interventions, particularly for people with severe obesity and greater impulsivity.