In order to assess the variability among histopathologists in grading cervical dysplasia, four experienced histopathologists examined the same set of 106 biopsy specimens and assigned them to one of five diagnostic categories. These were: no dysplasia, mild dysplasia, moderate dysplasia, severe dysplasia and carcinoma in situ. The histopathologists did not discuss the grading criteria beforehand. There was considerable disagreement among the pathologists: unweighted group kappa 0.28, weighted group kappa 0.56. It appeared that all grades of dysplasia were equally difficult to distinguish from adjacent categories. Various explanations for this interobserver variation are put forward.