Attention Deficit Hyperactivity Disorder (ADHD) is a developmental and psychiatric disorder that affects different aspects of an individual life, such as cognitive functions. ADHD comprise a complex symptomatology such as cognitive flexibility and inappropriate risk-taking. We aimed to compare cognitive flexibility and appropriate risk-taking of adults with and without ADHD. For this purpose, the Conners’ Adult ADHD Rating Scale (CAARS) was used to screen 580 students of Tehran University in Iran. Forty participants who scored highest in CAARS were invited to have a clinical interview with a trained psychiatrist. The diagnosis was made based on the Diagnostic and Statistical Manual of Mental Disorders (DSM–5), using the Wender Utah Rating Scale (WURS). Finally, thirty individuals were diagnosed with ADHD. Meanwhile, the 30 students with the lowest scores on the CAARS and General Health Questionnaire (GHQ) were included as the control group. The two groups then were compared using the Cognitive Flexibility Inventory (CFI) and the Iowa Gambling Task (IGT). The results of the one-way ANOVA indicated that scores of case group in the components of cognitive flexibility were significantly lower in the patients compared to the control group. Also, the ADHD group had lower scores concerning appropriate risk-taking and had a shorter reaction time. Findings of the current study might help to open further avenues in the rehabilitation of cognitive flexibility and controlling reward-seeking and risk-seeking impulses.