In the UK the incidence of malignant melanoma is increasing and more patients with thinner primary lesions are diagnosed earlier. Most patients with very thin melanoma (< 0.76 mm Breslow thickness) are cured by surgical excision, however, 2-18% relapse over 0-11 years with local or distant metastatic disease and may die. There are still no recognized prognostic or predictive, clinical, serological or molecular markers that accurately determine which of these very thin melanoma will relapse: the Breslow thickness remains the single most important prognostic factor for melanoma in general. Improved prognostic indicators are therefore needed for this rare, but important, unusually aggressive group, to better direct new invasive and expensive investigations and treatment. This article reviews the clinical and histological aspects of relapsing very thin melanoma and discusses the findings of several recent studies, including our own. There is no clinical or biological evidence to support either wide surgical excision or sentinel node biopsy in these patients.