Summary o 1. This monograph is based on a prospective study of more than 1500 patients with malignant melanoma treated in Queensland, Australia, since July of 1963. 2. Queensland has the highest incidence of malignant melanoma in the world—16 new cases per 100,000 of population per annum. 3. Mortality rates from melanoma are rising in all countries where they have been studied. 4. There is an association between sunlight and malignant melanoma. 5. There is a hereditability of liability to melanoma of about 11% in Brisbane. 6. There is a familial incidence of melanoma. In these families, the melanomas occur in a younger age group and are more likely to be multiple. 7. Trauma must be a rare cause of a benign nevus becoming malignant but is a significant factor in the dissemination of tumor cells from a pre-existing malignant melanoma. 8. Melanomas spread by direct extension, by the lymphatics and by the bloodstream. The lymph nodes are not effective barriers to the spread of tumor cells, which may enter the blood-stream directly. 9. A history of change in a pre-existing or newly developed mole often indicates the development of malignancy. The change may be an increase in size or elevation, or a change in color or surface characteristics. 10. The appearance of a malignant melanoma often is diagnostic. The over-all color commonly is black, but gray, blue, red or pale areas within the main area are characteristic. 11. Incisional or shave biopsy or treatment by electrocautery is contraindicated when malignant melanoma is suspected. 12. Frozen section diagnosis by an experienced histopathologist is remarkably accurate in the diagnosis of pigmented tumors. 13. There is no absolute answer to the question of how radically to excise a malignant melanoma. Each patient requires an individual judgment and the extent of the excision will depend on factors known to influence the prognosis, the anatomic site of the lesion and the sex of the patient. 14. Regional nodes draining a malignant melanoma of the skin should be excised if they are clinically involved or suspected to be so. However, there is no place for the routine removal of apparently normal regional lymph nodes. 15. The most common site for malignant melanomas in women is the lower limb and in men the trunk, and the maximal age incidence is between 35 and 49 years for both sexes. 16. Of 1187 patients with cutaneous malignant melanoma treated in Queensland, the age-adjusted cumulative 5-year survivals were 81.6% for both sexes—87.7% for women and 73.6% for men. 17. Patients survived best if their lesions were on the limbs and worst if they were on the trunk.