AIMS--To analyse the diagnostic differences in reporting tumour histopathology between a district general hospital and a regional oncology centre. METHODS--Tumour histopathology reports (n = 227) extracted from Bolton General Hospital files between 1988 and 1992 were compared with the corresponding Christie Hospital (oncology centre) reports, the same material having been seen at both hospitals. RESULTS--Diagnostic agreement existed in 77% of all cases. The incidence of major discrepancies was 8.37%. Of the diagnoses, 19 (36%) cases involved major discrepancies and 34 (64%) cases minor discrepancies. Most discrepancies occurred in the lymphoma group and involved subclassification of Hodgkin's and non-Hodgkin's lymphoma. Ki1 anaplastic large cell lymphoma and T cell rich B cell lymphoma were problematic diagnoses. The correct grading of follicle centre cell lymphomas using the Kiel classification was another problem area. In 19 cases certain aspects of immunohistochemistry produced discrepancies. In one case an incorrect diagnosis was made at the oncology centre and in another both centres gave an incorrect diagnosis. CONCLUSIONS--Areas of diagnostic difficulty mainly involve the subclassification of lymphomas. Review of tumour pathology by experts is recommended, at least in certain categories, to ensure correct diagnosis and uniformity in subclassification of tumours.