Psychologists and other therapists are seeing an increasingly large number of bilingual individuals. Such clients are a special challenge when there has been some type of brain injury or disease because of the seemingly unpredictable effect such disorders may have on language skills, impacting either or both of the client's languages and interfering with internal speech that plays a role in higher cognitive functions such as insight and awareness. While there are many clinical assumptions about which language will show the least impairment or recover the best, such suppositions based on clinical lore are often contradictory. A review of the literature finds that the outcome of brain injury may be influenced by factors such as cerebral representation of a secondary language, method of language acquisition, age of acquisition, premorbid language proficiency, and style of learning in an individual. Neuropsychological concepts that can explain these findings are examined, along with their implications for therapy, and rehabilitation.