Most Large language models (LLMs) adopt an autoregressive architecture, predicting the next word token based on the preceding context. While this approach is robust for language generation tasks such as writing and summarization, it has limitations for high-level reasoning tasks, such as prediction and decision-making. To overcome these limitations, we introduce a new method called Prediction-Augmented Generation (PAG). PAG can improve the generation quality and predictive accuracy of large language models in inference-driven tasks by integrating task-specific predictive models as external tools, enabling more structured and precise reasoning. Moreover, our method does not simply copy the inferences of a predictive model, but improves the inference results with knowledge from the large language model to create better predictions. We comprehensively evaluate our proposed method on diverse datasets for automatic diagnosis tasks requiring extensive domain knowledge and advanced reasoning.