Objective: The objective of this study was to attempt to differentiate between ADHD combined and inattentive subtypes using high-resolution brain SPECT imaging. Method: Participants included 1150 ADHD primarily inattentive type and 1193 ADHD combined type patients seeking at a clinic. The average age for both groups was 39.76 years (SD = 14.69), and consisted of 60.0% males and 40% females. The overall sample was comprised of 70.3% Caucasian, 2.4% Hispanic, 1.4% Asian 19.8% unknown. All participants underwent brain SPECT imaging at rest and during activation using semiquantitative visual readings. Results: A MANOVA was significant at the .05 level, Wilks' λ= .979; F(34, 2343) = 1.459, p = .042, revealing significant group differences between the combined and inattentive ADHD subtypes. The combined type group yielded significantly lower blood flow at baseline in the Occipital lobes and higher blood flow in the Cerebellum compared to the primarily inattentive type group at the .01 level. These results were not repeated during activation. Conclusion: Differences found in cerebral blood perfusion at baseline but not activation between ADHD subtypes is an important clinical finding as it demonstrates differential cerebral blood flow for these diagnostic sub groups The finding that combined type ADHD patients display hyperactive blood perfusion compared to inattentive type in the cerebellum is consistent with contemporary views that the cerebellum plays a major role in executive functioning and the motor aspects of sensory perception that derive from planning and other executive actions.