Santeria, a religious system that blends African and Catholic beliefs, is practiced by many Cuban Americans. One aspect of this system is the belief in spirit possession. Basic santeria beliefs and rituals, including the fiesta santera (a gathering at which some participants may become possessed), are briefly described, and four cases in which the patients' belief in possession played a role in their mental illness are presented. The belief in possession can complicate the diagnosis and treatment of mental illness, but it should not be considered a culture-bound syndrome. Rather, it may be a nonspecific symptom of a variety of mental illnesses and should be evaluated in the context of the patient's overall belief system and ability to carry out usual activities.