Clinicians ignore lengthy guidelines and prefer pocket cards and concise pamphlets. However, brevity in guidelines may lead to deficiency in quality. Our objective, therefore, was to examine the quality of brief guidelines produced by professional bodies, using those produced by the UK Royal College of Obstetricians and Gynaecologists (RCOG) as an example. We assessed all 22 'green-top' guidelines, produced by September 2002, for quality using a validated 37-item appraisal instrument. This instrument evaluated the guidelines on three dimensions, namely rigour of development, context and content and applicability. Ten (45%), 18 (82%) and five (23%) of the 22 guidelines met at least half the quality criteria for rigour of development, context and content and applicability, respectively. We conclude that the brief guidelines were deficient in several specific quality items, particularly those in the applicability dimension. Guideline developers need to achieve the higher quality standards expected of professional bodies.