SkinGPT-4 is an interactive dermatology diagnostic system based on multimodal large language models. It was developed by aligning a pre-trained vision transformer with the Llama-2-13b-chat large language model, using a vast collection of 52,929 skin disease images, clinical concepts, and doctors' notes. The system underwent a two-step training process to enhance its ability to diagnose skin conditions. SkinGPT-4 can analyze uploaded skin images, identify skin conditions, and provide interactive treatment recommendations. It was evaluated by 150 real-life cases with board-certified dermatologists, showing accurate diagnoses. SkinGPT-4 offers a 24/7 service, providing rapid responses and supporting local deployment to ensure user privacy. It helps reduce the burden on dermatologists and improves access to dermatological care, especially in underserved areas. However, it is not a substitute for professional medical advice. The system's performance was consistent across multiple evaluations, and it demonstrated strong diagnostic capabilities for various skin conditions. Despite its advantages, challenges remain, including the need for more diverse datasets and the potential for hallucinations in LLMs. SkinGPT-4 is designed to assist dermatologists and patients, providing valuable insights and improving the overall quality of dermatological care. The system is publicly available for research and non-commercial use, with code and data accessible through specified links.SkinGPT-4 is an interactive dermatology diagnostic system based on multimodal large language models. It was developed by aligning a pre-trained vision transformer with the Llama-2-13b-chat large language model, using a vast collection of 52,929 skin disease images, clinical concepts, and doctors' notes. The system underwent a two-step training process to enhance its ability to diagnose skin conditions. SkinGPT-4 can analyze uploaded skin images, identify skin conditions, and provide interactive treatment recommendations. It was evaluated by 150 real-life cases with board-certified dermatologists, showing accurate diagnoses. SkinGPT-4 offers a 24/7 service, providing rapid responses and supporting local deployment to ensure user privacy. It helps reduce the burden on dermatologists and improves access to dermatological care, especially in underserved areas. However, it is not a substitute for professional medical advice. The system's performance was consistent across multiple evaluations, and it demonstrated strong diagnostic capabilities for various skin conditions. Despite its advantages, challenges remain, including the need for more diverse datasets and the potential for hallucinations in LLMs. SkinGPT-4 is designed to assist dermatologists and patients, providing valuable insights and improving the overall quality of dermatological care. The system is publicly available for research and non-commercial use, with code and data accessible through specified links.