Purpose: This case study describes the language evaluation and treatment of a 5-year-old boy, Lucas, who is Deaf, uses American Sign Language (ASL), and presented with a language disorder despite native access to ASL and no additional diagnosis that would explain the language difficulties. Method: Lucas participated in an evaluation where his nonverbal IQ, fine motor, and receptive/expressive language skills were assessed. Language assessment included both formal and informal evaluation procedures. Language intervention was delivered across 7 weeks through focused stimulation. Results: Evaluation findings supported diagnosis of a language disorder unexplained by other factors. Visual analysis revealed an improvement in some behaviors targeted during intervention (i.e., number of different verbs and pronouns), but not others. In addition, descriptive analysis indicated qualitative improvement in Lucas' language production. Parent satisfaction survey results showed a high level of satisfaction with therapy progress, in addition to a belief that Lucas improved in language areas targeted. Conclusions: This study adds to the growing body of literature that unexplained language disorders in signed languages exist and provides preliminary evidence for positive outcomes from language intervention for a Deaf signing child. The case described can inform professionals who work with Deaf signing children (e.g., speech-language pathologists, teachers of the Deaf, and parents of Deaf children) and serve as a potential starting point in evaluation and treatment of signed language disorders.