In a period of 18 months, 187 cytology aspiration biopsies of the breast were performed at the Centre François Baclesse by clinicians and radiologists, using the conventional technique. Comparison of the results with clinical, radiological and histological findings by different specialists showed that one out of two aspiration biopsies gave an erroneous diagnosis. The authors believe that this failure was due to the fact that the biopsies were not performed by a cytologist. This prime condition of success should be more clearly expressed in the literature.