Proliferation of clinical guidelines has given rise to a number of concerns about the status of clinical advisory statements. Are guidelines advisory or mandatory? What regulatory functions do guidelines serve; do they allow clinical discretion a large enough role? Relationships between legislation and guidelines, and the way courts go about determining the legal status of guidelines, are explained. The following questions in the context of the law of negligence are addressed. Do doctors who deviate from guidelines place themselves at increased risk of being found liable in negligence if patients suffer injury as a result? Could compliance with guidelines protect health care workers from liability in such circumstances? What legal responsibility do the developers and issuers of guidelines have if their guidance is found to be faulty? Common law cases featuring clinical guidelines or protocols have been identified from the database Lexis, which searches the full text of the transcripts and reports of court cases in UK, Commonwealth and United States jurisdictions. Secondary literature, identified from the bibliography of clinical guidelines maintained by the Department of Health Services Research at the University of Aberdeen (assembled from DHSS-DATA, Embase, Grateful Med, Medline and SIGLE) has also been consulted. The legal status of a guideline turns on whether its development and application have statutory backing, and whether the guideline embodies clinical practices accepted as proper by a responsible body of doctors. The mandatory effects of guidelines can be gauged, to some extent, by the sanctions that apply in the event of non-compliance. US courts have ruled that guideline developers can be held liable for faulty guidelines, and that doctors cannot pass off their liability by claiming that adherence to guidelines has corrupted clinical judgement. Protocols and guidelines provide the courts with examples of clinical standards across a wide range of medical practice. As guidelines proliferate, so they will increasingly be used in court. However, adherence to guidelines has not automatically been equated with reasonable practice, and the courts seem unlikely to follow the standards enunciated in clinical guidelines without critically evaluating their authority, flexibility and scope of application.