BACKGROUND: The vaginal vault smear is a test for cellular atypia in women who have undergone a hysterectomy. In asymptomatic women the test has poor sensitivity and specificity. Current guidelines recommend: vault smears should not be used after hysterectomy for benign pathology; two vault smears (6 and 12 months postsurgery) should be taken when there is evidence of completely excised CIN II/III in the specimen. AIM: To describe primary health care professionals' self-reported knowledge and behaviour relating to the use of vault smears. DESIGN OF STUDY: Questionnaire. SETTING: South Birmingham. METHODS: Postal questionnaire survey to primary health care professionals (general practitioners and practice nurses, n = 424). Results: Response rate 80.0%, completed response rate 68.9%. Mean knowledge score was 7.3 out of possible 12 (SD 1.9); range 0-10. No significant differences were observed between GPs and practice nurses in knowledge scores, although differences were noted in the frequency of performing vault smears. An inverse relationship was observed between frequency of performing vault smears and level of knowledge about the test. There was a positive association between requesting further information and the 'knowledge score'. Only 11% correctly answered a question based on current guidelines. CONCLUSIONS: Knowledge of current guidelines was poor. Those who undertook fewest vault smears appeared best informed. This suggests that if all primary care professionals practised according to current guidelines, the number of vault smears performed may be reduced. Unnecessary vault smears may cause additional anxiety in women and have financial consequences for the NHS.