We report a rare case of giant metastatic malignant melanoma (GMMM). A 52-year-old man had noticed a small nodule on the top of his head about one year previously. When he visited our hospital on March 18, 1998, the dome-shape nodule measured 30×30mm and was accompanied with satellite lesions. Excisional biopsy of satellite lesion yielded a histopathological diagnosis of malignant melanoma (MM). There were no findings of systemic metastasis. We classified this as MM (pT4bN0M0, Clark level V, Stage III) . After we injected IFN β into the lesion, we perfomed wide local excision. However, in this case, cutaneous metastasis appeared on the left neck 5 months lates MM. He had received DAV-IFN β therapy for the lesion. However, after three courses of adjuvant therapy, the neck metastasis did not decrease. He died of the disease one year and 9 months after the operation. Very few cases of GMMM have been reported to gradually enlarge reaching a size of 330×220×115mm. [Skin Cancer (Japan) 2000; 15: 147-151]