OBJECTIVE: Although intracranial aneurysms (IAs) are a major public health problem in the United States, few etiological factors are known. Most aneurysms remain asymptomatic until they rupture, producing subarachnoid hemorrhage, one of the most severe forms of stroke. Despite the technical advances in endovascular and microsurgical treatment, these patients still have high mortality and morbidity rates. Hence, the biology of aneurysm formation and growth is of intense interest. The presence of T and B lymphocytes, as well as macrophages, in human IA tissues suggests a role for inflammation in IA pathogenesis. However, the types of cytokines that are involved and regulated during cerebral aneurysm formation and growth are not known. To study the underlying pathogenesis of IA, we analyzed the expression of cytokines that participate in proinflammatory and anti-inflammatory responses.