Background: Attention deficit hyperactivity disorder (ADHD) was long considered to be limited to children and adolescents, but it is now known that ADHD symptoms may persist into adulthood. It is plausible that the etiology of ADHD is not one-dimensional, but instead involves various neuroanatomical and neurochemical systems, with the causes of the main abnormalities believed to be catecholaminergic. Iodine-123-labeled meta-iodobenzylguanidine (¹²³I-MIBG) is a physiological analogue of norepinephrine (NE). To the best of our knowledge, there are no reports about the abnormalities of MIBG scintigraphy in patients with ADHD. The cases presented are male adult patients with different comorbid psychiatric disorders. Case presentation: The cases presented are male adult patients with different psychiatric disorders. Case 1 was a 52-year-old male residential construction foreman, who had been diagnosed with acute schizophrenia-like psychotic disorder. ¹²³I-MIBG planar and SPECTs of the studies were performed at 20 min (early phase) and 3 h (late phase) after intravenous injection of 111 MBq. Planar images were processed to determine the heart (H) to mediastinum (M) ratio (H/M). The early and late H/M ratios were 1.22 and 1.07, respectively. Case 2 was a 52-year-old male civil servant who was diagnosed with adjustment disorder. The early and late H/M ratios were 1.98 and 2.08, respectively. Conclusion: Clinical studies make it clear that symptoms of ADHD are more heterogenous and subtle in adults than children. Adult ADHD is significantly commorbid with wide range of other 12-month disorders. MIBG imaging can be useful to diagnose patients with preexisting psychiatric disorders and ADHD. It might be possible to diagnose objectively though the psychiatric statuses resemble or coexist with other psychiatric disorders. Needless to say, further research is important.