Malignant melanoma is an aggressive tumor of melanocytes whose primary function is producing melanin pigment. Though they vary according to the microscopical subtype, these tumors often arise in the sun-exposed skin of elderly individuals, in the acral regions and in the palms and soles of the hands and feet. A 56-year-old patient visited the emergency department of our hospital with complaints of a sudden hemorrhage from a mass on her left thigh which had appeared five months ago. On physical examination a brown-black mass with dimensions of 18 x 16 x 5 cm, protruding from the skin with a partially and actively hemorrhagic, ulcerated surface, was found on the left gluteal region. The mass was excised surgically with 3 cm safe surgical margins. Histopathologically the lesion was diagnosed as "nodular malignant melanoma - Clark level 5". A malignant melanoma of such a large size is very exceptional in the literature; thus it is presented here with its interesting rapid clinical course.