The records of all patients who had a C3 result on fine needle aspiration cytology (FNAC) over a 3-year period were reviewed. Clinical and mammographic findings at presentation were correlated with histopathological diagnosis. Of 43 patients, 32 patients underwent excision biopsy. Histology was benign in 25 patients, eight patients had an invasive breast carcinoma, two a phyllodes tumour and one had widespread ductal carcinoma in situ (DCIS). All but two of the patients with invasive tumours had abnormalities on clinical examination or imaging. In two patients there was no clinical or mammographic suspicion of malignancy. A C3 breast cytology result must be taken seriously as it is frequently an indicator of underlying malignancy. These results suggest that definite histology should be obtained in all patients because of the unacceptably high false-negative rate of clinical and radiological assessment in this group.