An influential model holds that obsessive–compulsive disorder is caused by distinctive personality traits and belief biases. But a substantial number of sufferers do not manifest these traits. I propose a predictive coding account of the disorder, which explains both the symptoms and the cognitive traits. On this account, OCD centrally involves heightened and dysfunctionally focused attention to normally unattended sensory and motor representations. As these representations have contents that predict catastrophic outcomes, patients are disposed to engage in behaviors and mental (...) rituals designed to forestall these outcomes or to produce more precise information. The same representations also cause the cognitive traits characteristic of sufferers. (shrink)