Self-injurious behavior (SIB) is common among people with severe mental retardation who may also have multiple complex medical problems coupled with communication difficulties. This combination of factors sometimes makes it difficult to obtain accurate and detailed medical histories. In this exploratory descriptive study of 25 patients with SIB, 28% had previously undiagnosed medical conditions that could be expected to cause pain or discomfort. Six of the 7 patients experienced decreased SIB with treatment of their medical conditions. In patients with SIB, impaired communication skills, and complex medical histories, medical conditions that may be associated with pain or discomfort must be a consideration in determining the etiology of the SIB.