OBJECTIVE: To evaluate the efficiency of the criteria proposed by the National Referral Guidelines at selecting patients with lower gastrointestinal tract cancer for urgent outpatient assessment when compared with the standard method for prioritization. PATIENTS AND METHODS: Consecutive patients aged 50 and over referred to a colorectal unit were offered urgent or non-urgent outpatient appointments on the basis of the contents of the referral letter. Clinical information obtained during the outpatient consultation was used to identify those patients that satisfied the guideline criteria for urgent referral. Patients were investigated and the findings recorded. RESULTS: Of 247 patients who completed their investigations 18 were found to have lower gastrointestinal tract cancer. Urgent outpatient appointments were offered to 115 patients of whom 14 had cancer (P = 0.0067, sensitivity=78%). A total of 119 patients satisfied the guideline criteria for urgent referral, including 17 of the patients who were found to have cancer (P < 0.0001, sensitivity=94%). CONCLUSION: The criteria used in the guidelines provide an effective method for selecting patients with cancer for urgent assessment. Application of the guidelines by general practitioners can be recommended.