In this paper, we compare and contrast Medical Informatics (MI) and Bioinformatics (BI), and provide a viewpoint on their complementarities and potential for collaboration in various subfields. We compare MI and BI along several dimensions, including: (1) Historical development of the disciplines, (2) Their scientific foundations, (3) Data quality and analysis, (4) Integration of knowledge and databases, (5) Informatics tools to support practice, (6) Informatics methods to support research (signal processing, imaging and vision, and computational modelling, (7) Professional and patient continuing education, and (8) Education and training. We point out that, while both disciplines differ in their history, scientific foundations and methodological approaches to research in various areas, they nevertheless share methods and tools, which provides a basis for exchange of experience in their different applications. MI expertise in developing health care applications and the strength of BI in biological discovery science complement each other well. The new field of Biomedical Informatics (BMI), holds great promise for developing informatics methods that will be crucial in the development of genomic medicine. The future of BMI will be strongly influenced by whether significant advances in clinical practice and biomedical research come about from separate efforts in MI and BI, or from emerging, hybrid informatics subdisciplines at their interface.