The lifetime prevalence rate of obsessive-compulsive disorder (OCD) is more than 2 percent of the population. Its contemporary pathophysiological models have been explored. As serotonin reuptake inhibitors and cognitive behavior therapy are both considered first-line treatments of OCD, the treatment interventions provide us with clues. In this review, the authors summarized that genetics, neuropathology in the cortico-striatal-thalamic-cortical (CTSC) circuits, the association between OCD and Tourette's syndrome, the possibility of autoimmune-mediated pathophysiology containing PANDAS, serologic surveys of patients, and animal models including transgenic mice. Further research, genetic, neuroimmunological, and neuroimaging works may ultimately be useful in developing new treatments of OCD.