Objective: Previous research shows an association between obesity and attention deficit hyperactivity disorder (ADHD). The present study compares pre- and post-bariatric surgery patients using the internationally used Conners' Adult ADHD Rating Scale (CAARS™) to screen for ADHD. Methods: Matched samples pre- (N = 120) and post-bariatric surgery (N = 128) were compared using self-rating instruments to assess ADHD-relevant symptomatology, depression, eating-related psychopathology, and BMI. Results: Prevalence of probable ADHD did not differ between groups using the CAARS Index Scale T-scores; however, CAARS subscales Inattention/Memory and Self-Concept showed significantly lower scores in post-surgery patients. All CAARS subscales correlated significantly with each other, with depression and eating-related psychopathology. There was no correlation between ADHD and excess BMI loss in post-surgery patients. Conclusion: The findings suggest that a considerable number of patients before and after bariatric surgery screened positive for ADHD. It can be hypothesized that some core ADHD symptoms improve after surgery. Future studies are warranted to investigate the influence of ADHD on long-term surgery outcomes.