OBJECTIVE: To compare overall and methodological quality with content in national and supra-national Clinical Practice Guidelines (CPGs) on benign prostatic hyperplasia (BPH) and lower urinary tract symptoms (LUTS), as the purpose of CPGs is to reduce unwanted variation in practice and improve patient care by setting agreed standards based on the best available evidence. METHODS: An electronic search was used to identify Internet-based national and supra-national CPGs on BPH and LUTS available in 2001. Two independent assessors analysed the content and appraised the methodological quality of the CPGs using an existing and validated instrument (St. George's Hospital Medical School Health Care Evaluation Unit Appraisal Instrument) comprising 37 items grouped into three broad areas, i.e. rigour of development, context and content, and clinical application. RESULTS: Eight CPGs were suitable for appraisal; there was much variation in overall and methodological quality. There was agreement that a patient history and physical examination (including a digital rectal examination) should be used in all symptomatic men. In addition, patients' symptoms should be assessed using a validated symptom score, e.g. the International Prostate Symptom Score. There was considerable variation in the number and type of diagnostic tests recommended for routine assessment. CPGs scoring low on the appraisal instrument (indicating poor overall and methodological quality) were more likely to recommend more diagnostic tests than those scoring high. There was general agreement between the guidelines on the treatment of BPH/LUTS and the importance of the patient's involvement in making management decisions. Guideline quality was independent of local health resources and publication year. CONCLUSION: The overall and methodological quality of CPGs on BPH/LUTS varies considerably. There appears to be an inverse relationship between guideline quality and the number of diagnostic tests recommended for routine assessment. Using CPGs of high quality may prevent men with BPH/LUTS being exposed to tests of doubtful utility. Although this may reduce both resource use and exposure to potential harm, moving to a more minimalist approach to diagnosis may itself be potentially harmful to patients.