A young woman presented with bilateral ovarian tumours. Multiple sections of each tumour were shown to many pathologists for consultation; some considered the tumours to be borderline, whereas others thought that one or both of them was malignant. Morphometry showed that the numerical classification probabilities for borderline tumour were 0.78 for the left ovarian tumour and 0.85 in the right. The lesions were therefore regarded as borderline tumours and no additional chemotherapy was given. Three years after the second operation the patient is alive and well without clinical or biochemical evidence of recurrence. Most patients with borderline tumours who die from the disease do so in the first two years after the operation. This young patient was prevented from severe overtreatment by the application of morphometry, illustrating its use in this area of diagnostic gynaecopathology.