In this article we present grids as an architecture for medical image processing and health-care networks. We argue that confidential patient data should not be stored on the grid unprotected and explain why access control systems do not offer sufficient protection alone. Effective protection can be achieved by storing confidential data in encrypted form. Our proposal details a key management architecture, that allows encrypted storage and still enables users to access decryption keys for data they are authorized to see. Furthermore our architecture is robust against breakdowns, and denial of service attacks. It scales well with the number of users and does not introduce a single point of failure into the system.