In years past, OCD was believed to be psychological in origin. Now, it's a virtual certainty that it's a neurological condition. For one thing, OCD often runs in families, and it's less than likely that family members, including cousins, grandchildren, and others not living in the same household, would share a single neurosis. Also, the demonstrated worsening of OCD symptoms in some children following strep infections (and in older adults following other illnesses) suggests that the condition has a physical cause. Finally, modern brain-imaging techniques have revealed vastly different brain activity in patients who have OCD than in those who do not.