The storage and manipulation of digital images and the analysis of the information held in those images are essential requirements for next-generation medical information systems. The medical community has been exploring collaborative approaches for managing image data and exchanging knowledge and Grid technology [1] is a promising approach to enabling distributed analysis across medical institutions and for developing new collaborative and cooperative approaches for image analysis without the necessity for clinicians to co-locate. The EU-funded MammoGrid project [2] is one example of this and it aims to develop a Europe-wide database of mammograms to support effective co-working between healthcare professionals across the EU. The MammoGrid prototype comprises a high-quality clinician visualization workstation (for data acquisition and inspection), a DICOM-compliant interface to a set of medical services (annotation, security, image analysis, data storage and querying services) residing on a so-called Grid-box and secure access to a network of other Grid-boxes connected through Grid middleware. One of the main deliverables of the project is a Grid-enabled infrastructure that manages federated mammogram databases across Europe. This paper outlines the MammoGrid Information Infrastructure (MII) for meta-data analysis and knowledge discovery in the medical imaging domain.