- BACKGROUND: Melanoma prognosis is dependent upon early recognition and treatment. There is a need for good clinical guidelines that focus on the early signs of melanoma. The ABCD (asymmetry, border, colour and diameter) rule states that most melanomas are more than 6 mm in diameter. Critics crave a modification, arguing that small diameter melanomas are not infrequent. OBJECTIVES: The aim of the present study was to describe the frequency and prognosis of melanomas less than 7 mm in a clinical setting. METHODS: The Norwegian Melanoma Project was conducted as a multicentre, prospective study with inclusion criteria. Patients were recruited from five dermatological departments in Norway from 1990 to 1993. RESULTS: The frequency of small melanomas was 11.4% (18/158). One-third was in situ melanoma, the rest invasive with a median thickness of 0.8 mm. Four small melanomas were T2 lesions, with a Breslow thickness of more than 1 mm. One nodular T2 melanoma recurred locally 2 years after diagnosis and the patient died of distant metastasis only months later. CONCLUSIONS: The ABCD rule remains a practical guide for early recognition of melanoma. Clinicians must be aware of its limitations.