The following case of a retroperitoneal fibrolipoma is so typical of this rare form of abdominal tumor, at the present time receiving in general but indefinite recognition and differentiation, that it seems to justify a detailed presentation. On account of the necessity for anticipating the malignant degeneration to which all such connective tissue tumors are more or less prone, as well as preventing the serious involvement of various organs even by a benign overgrowth, an early diagnosis is of great importance. This, in view of the frequent paucity of symptoms and obscure local signs, is difficult and but infrequently made before the condition has rendered an operation impossible or extremely hazardous. In 1897 Adami 1 gave the immediate mortality from operation of the twenty-six instances he was able to collect at 53.9 per cent. One recurrence increased the mortality to 57.7 per cent. I have collected in addition to these three