Developers of Clinical Decision Support Systems (CDSSs) have to date been more concerned with the efficacy of systems (e.g. measurable improvements in clinical outcomes) than with safety (e.g. potential for harmful side-effects). In future CDSS developers will be required (by the courts etc.) to acknowledge a "duty of care" covering all aspects of design, development and deployment. Experience in the transport, power and other safety-critical industries has led to a range of quality and safety assurance methods whose adoption may be needed before CDSSs can safely become an integral part of routine patient care, and before the trust of healthcare professionals, patients and other stakeholders can be gained. No single method will be sufficient for safe development and deployment; a range of techniques will be needed and used selectively. This paper is a contribution to discussion of quality, safety and legal liability issues in the medical informatics community.