We present the differential diagnosis and treatment of Frank, a 26-year-old man with LandauKleffner syndrome (LKS). At the time of assessment, Frank was no longer suffering from primary symptoms of LKS; however, he presented with significant social and behavioral difficulties including social anxiety and social skills deficits. Frank participated in Social Effectiveness Therapy (SET), an empirically supported, multi-component behavioral treatment program aimed at reducing social anxiety and improving social functioning. Although Frank exhibited significant reductions in social anxiety at post-treatment, functional behavioral assessment of social behavior suggested that Frank continued to experience social difficulties (e.g., speech length, latency to respond, rigidity in interactions). It appears that the application of an empirically supported treatment such as SET may result in attenuated treatment effects when social anxiety is secondary to a neurological condition such as LKS. Treatment needs for secondary symptoms of LKS are discussed.