The incidence, prevalence, and mode of presentation of cavernous malformations is important to better understand the disease, educate patients and practitioners, aid in treatment decisions, and to design clinical trials. Prior to the advent of MRI, cavernous malformations were often diagnosed only when a catastrophic event occurred and/or the lesion was removed. With the more frequent diagnostic use of MRI, it has become clear that cavernous malformations are more prevalent than previously thought and many are identified incidentally. The remainder may present to clinical attention with intracerebral hemorrhage, seizure without hemorrhage, or focal neurologic deficit without overt hemorrhage. The precise reason why some cavernous malformations become symptomatic and others remain asymptomatic is not clear. However, evolving data suggests that brainstem location, estrogen use in women, and low vitamin D may play a role in hemorrhagic presentation.