This book constitutes the refereed proceedings of the First International Workshop on Machine Learning in Medical Imaging, MLMI 2010, held in conjunction with MICCAI 2010, in Beijing, China, in September 2010. The 23 revised full papers presented were carefully reviewed and selected from 38 submissions. The papers address topics such as machine learning applications to medical images, medical image analysis, multi-modality fusion, image reconstruction for medical imaging, computer-aided detection/diagnosis, medical image retrieval, cellular image analysis, molecular/pathologic image analysis, and dynamic, functional, physiologic, and anatomic imaging.