BACKGROUND Several guidelines exist on the appropriate use of serum tumour markers in the management of patients with cancer. This study audited tumour marker requesting against these guidelines in a busy teaching hospital over a 12-month period. METHODS All marker requests from 1 April 2001 to 31 March 2002 were collected using the laboratory computer. From one 24-h period, the case notes from all hospital requests [excluding prostate-specific antigen (PSA)] were examined. RESULTS Tumour marker workload increased by 125% from 1997-98 to 2001-02. Of 27 323 tumour marker requests, 7166 were from general practice, 2312 were requested on hospital admission before further investigation, 612/3636 of CA125 and 98/374 of CA15.3 requests were on men and 12/11585 PSA requests on women. Of 34 case notes examined, 18 had tumour markers measured before biopsy and only nine after. Of 19 patients with 'normal' markers, one had malignancy on biopsy and, of 15 with one or more raised markers, four had normal biopsies. CONCLUSIONS Tumour marker workload is rapidly increasing. Tumour markers are frequently and inappropriately requested, either because they are on patients of the wrong sex, or because they are taken before a cancer diagnosis is reached. Results from these tests can be falsely reassuring or unduly alarming.