Medical and clinical audit are tools introduced in an attempt to assess clinical performance. Clinical audit implementation in practice should follow that of the audit and the learning cycles. Ideally, audit should assess the outcome of clinical care. However, many audit projects concentrate on the process of care, which is more amenable to review. One of the cornerstones of audit is the setting up of agreed standards of care. This takes the form of clinical practice guidelines derived, preferably from the outcome of randomised double-blind controlled trials as the basis of evidence-based medicine. The assessment of the contribution of the clinical laboratory to patient outcome could be seen as a further extension of clinical audit in the practice of laboratory medicine. Areas where this contribution may be assessed include validity and usefulness of diagnostic tests, the assessment of analytical goals in relation to patient outcome, variation in inter-laboratory performance and its effect on decision limits and whether any measurement or set of measurements contribute to improved outcome. The practice of clinical audit and the application of evidence-based medicine are seen as powerful educational tools, though there is much work to be done to assess their contribution to clinical outcome. Randomised clinical trials could form the basis for the assessment of the value and contribution of the laboratory to the outcome.