We report a case study of cognitive linguistic treatment in a teenager with chronic severe Landau Kleffner Syndrome. The effect of speech and language therapy in LKS is rarely examined and our case is unique in that we use an effective approach in adult aphasia to treat language deficits in aphasia in LKS. The results show successful acquisition of a considerable amount of new words as well as improved communication in daily life. However, auditory verbal agnosia, the most prominent feature in LKS, persisted. Cognitive linguistic treatment seems a promising treatment to improve spoken language production in LKS, but more research is needed to optimize speech and language therapy of auditory verbal agnosia and auditory language comprehension in children with LKS.