Because neoadjuvant therapy, including preoperative chemotherapy and tamoxifen, is becoming increasingly common for early breast cancer, it is desirable to grade tumours before surgery so that the most appropriate medical regimen can be selected. We have used a cytological grading system for ductal carcinoma of type not otherwise specified (NOS). Wet-fixed Papanicolaou-stained breast aspirates are examined for the extent of cell dissociation, cell size and uniformity, and the appearance of nucleoli, the nuclear margin, and chromatin. 377 invasive breast carcinomas were removed after preoperative diagnostic fine-needle aspiration cytology (FNAC) during the 25 months of the study. 286 tumours were ductal carcinomas NOS on histology. We established three cytological grades and found that cytological grade corresponded well with the established histological grades (Elston's modified Bloom and Richardson method). All cytological features included in the score were equally important on regression analysis. This study shows that grading of breast cancer on FNAC is feasible and reproducible. Cytological grade may substitute for histological grade, so a combination of FNAC and mammography can provide information on tumour type, grade, and size before surgery. We recommend this grading system to centres that use FNAC for the diagnosis of breast cancers.