Malignant melanoma in soft parts is rare and no cases of malignant melanoma occuring from mesocolon have been reported in the previous literatures. A 2-year-ll-month-old girl with malignant melanoma originated from the transverse mesocolon was reported. The tumor, measured 7x7x5 cm in size and 110g in weight, was removed with part of transverse colon and regional lymphnodes. The histological findings revealed nest-formed large clear cells with vesicular nuclei and prominent nucleoli, some of the neoplastic cells had melanin pigment. Mature melanosomes in the cytoplasm of neoplastic cells were demonstrated by electron microscopy. The patho-logical diagnosis was malignant melanoma of soft parts. This case was considered primary occurence of the transverse mesocolon because no other melanotic lesion was found in other part of her body.
