[Not diagnosable malignant melanomas].

Of the 3574 malignant melanomas treated in Hornheide between December 1981 and August 1990 (not including preinvasive cases) 97 were not immediately recognized. These tumours did not look like melanomas. In 72% they were smaller than 10 mm in diameter, and in 20%, smaller than 5 mm. Clark's so often quoted "pencil rule" should no longer be used as an aid to exclusion of invasive melanoma. Localization of the unrecognized melanomas was on the head and neck in 22% of cases. In 37%, the patients were under the age of 40 years. No less than 25% of the patients had multiple melanomas. Many of these melanomas. Many of these melanomas were thin tumours (less than 0.75 mm in 55% and less than 1.5 mm in 77%). This explains why more than 50% of the lesions are described as "macules". The most common incorrect diagnoses were dysplastic naevi (44%) and common (23%) naevi. The most important anamnestic criteria are the patients' own statements about changes in size, colour and shape. These "dynamic" elements must be more carefully observed and documented during process of the clinical diagnosis.