In this retrospective study, the feasibility and implementation of a clinical guideline was evaluated in 130 consecutive patients with chronic urticaria. We analysed how often a questionnaire was used, how often routine laboratory tests were performed and on what information (history-taking, detailed questionnaire, laboratory or provocation tests) the diagnosis was made. In this validation sample, the number of identified diagnoses was compared with the number of identified diagnoses of a prospective study previously performed in the same hospital. A cause was identified in 58 patients (45%): 43 of these had physical urticaria and 15 had chronic urticaria. In 50 of the 58 patients (86%) the cause was identified by history-taking and in 8 patients by additional use of the questionnaire. In 38 patients the questionnaire was not in the patient's file. In 89 of 130 patients (68%), laboratory tests were performed without a reason suggested by the patients' history. This did not reveal a cause in any patient. In general, the diagnostic guideline was followed reasonably well. In identifying a cause of urticaria, careful history-taking was important; routine laboratory tests were not helpful. A detailed questionnaire is presented in an appendix.