The 4th International Workshop on Medical Imaging and Augmented Reality, MIAR 2008, was held at the University of Tokyo, Tokyo, Japan during August 1-2, 2008. The goal of MIAR 2008 was to bring together researchersin medical imaging and intervention to present state-of-the-art developments in this ever-growing research area. Rapid technical advances in medical imaging, including its gr- ing application in drug/gene therapy and invasive/interventional procedures, have attracted signi?cant interest in the close integration of research in the life sciences, medicine, physical sciences, and engineering. Current research is also motivated by the fact that medical imaging is moving increasingly from a p- marily diagnostic modality towards a therapeutic and interventional aid, driven by the streamlining of diagnostic and therapeutic processes for human diseases by means of imaging modalities and robotic-assisted surgery. The impact of MIAR on these ?elds increases each year, and the quality of submitted papers this yearwas veryimpressive. We received90 full submissions, which were subsequently reviewed by up to ?ve reviewers. Reviewer a?liations were carefully checked against author a?liations to avoid con?icts of interest, and the review process was run as a double-blind process. A special procedure was also devised for papers from the universities of the organizers, upholding a double-blind review process for these papers. The MIAR 2008 Program C- mittee ?nally accepted 44 full papers. For this workshop, we also included three papers from the invited speakers coveringregistration and segmentation, virtual reality, and perceptual docking for robotic control.