Using Sleep Medicine guidelines and textbook, we evaluated four large language models (LLMs) (Llama 3.2 3B, Llama 3.3 70B, GPT 4o mini, Gemini 2.0 Flash) on AIMS certification questions, comparing baseline and Retrieval Augmented Generation (RAG) performance. RAG improved accuracy in all models (e.g., Llama 3.2 +9.6 points, Gemini 2.0 +4.0 points), highlighting RAG's role in enhancing LLM reliability in specialized medical domain.