Aphasia is a language disorder that results from damage to portions of the brain that are responsible for language. Strokes are the most common cause of aphasia, although aphasia can also result from a brain tumor, infection, head injury, or dementia that damages the brain. Individuals with aphasia have difficulty speaking—both in producing words and complete sentence structure—or understanding speech, or both.

Depending on the severity of the aphasia (and the degree of permanent brain damage), some patients regain their speech capabilities with little or no rehabilitation. In most cases, however, speech therapy is necessary to regain language capabilities.