BACKGROUND: Solitary fibrous tumor (SFT) arises in many parts of the body, but rarely in the kidney. To the best of our knowledge this is the second report of a fatforming SFT in the kidney. CASE: We present a case of a fat-containing SFT at the parihilar region of the kidney in a 64-year-old man complaining of epigastric pain. The tumor was initially diagnosed as angiomyolipoma at hematoxylin and eosin stains. However, by immunohistochemistry the tumor was reclassified as a fat-forming SFT. CONCLUSION: SFT arises in many sites, but rarely in the kidney. There is also a subset of these tumors that have a variable amount of adipocytic component that should be differentiated from angiomyolipoma. That subset of tumors affects mainly middle-aged adults of either gender and has a wide anatomic distribution. Recurrence is infrequent, and morphologically malignant examples are extremely rare.365295298Klemperer, P., Rabin, C.B., Primary neoplasms of the pleura: A report of five cases (1931) Arch Pathol, 11, pp. 385-412Chan, J.K.C., Solitary fibrous tumor-everywhere, and a diagnosis in vogue (1997) Histopathology, 31, pp. 568-576Bozkurt, S.U., Ahiskali, R., Kaya, H., Demir, A., Ilker, Y., Solitary fibrous tumor of the kidney (2007) APMIS, 115, pp. 259-262Hirano, D., Mashiko, A., Murata, Y., Satoh, K., Ichinose, T., Takahashi, S., Jike, T., Sugitani, M., A case of solitary fibrous tumor of the kidney: An immunohistochemical and ultrastructural study with a review of the literature (2009) Med Mol Morphol, 42, pp. 239-244MacLennan, G.T., Cheng, L., Solitary fibrous tumor of the kidney (2009) J Urol, 181, pp. 2731-2732Gelb, A.B., Simmons, M.L., Weidner, N., Solitary fibrous tumor involving the renal capsule (1996) Am J Surg Pathol, 20, pp. 1288-1295Guillou, L., Gebhard, S., Coindre, J.M., Lipomatous hemangiopericytoma: A fat-containing variant of solitary fibrous tumor? Clinicopathologic, immunohistochemical, and ultrastructural analysis of a series in favor of a unifying concept (2000) Hum Pathol, 31, pp. 1108-1115Yamaguchi, T., Takimoto, T., Yamashita, T., Kitahara, S., Omura, M., Ueda, Y., Fat-containing variant of solitary fibrous tumor (lipomatous hemangiopericytoma) arising on surface of kidney (2005) Urology, 65, p. 175Gengler, C., Guillou, L., Solitary fibrous tumour and haemangiopericytoma: Evolution of a concept (2006) Histopathology, 48, pp. 63-74Guillou, L., Fletcher, J.A., Fletcher, C.D.M., Extrapleural solitary fibrous tumour and hemangiopericytoma (2002) World Health Organization Classification of Tumours: Pathology and Genetics of Tumours of Soft Tissue Tumours and Bone, pp. 86-90. , Edited by CDM Fletcher, KK Unni, F Mertens. Lyon, IARC PressFine, S.W., McCarthy, D.M., Chan, T.Y., Epstein, J.I., Argani, P., Malignant solitary fibrous tumor of the kidney: Report of a case and comprehensive review of the literature (2006) Arch Pathol Lab Med, 130, pp. 857-861Lee, J.C., Fletcher, C.D.M., Malignant fat-forming solitary fibrous tumor (so-called "lipomatous hemangiopericytoma"): Clinicopathologic analysis of 14 cases (2001) Am J Surg Pathol, 35, pp. 1177-1185Park, S.B., Park, Y.S., Kim, J.K., Kim, M.H., Oh, Y.T., Kim, K.A., Cho, K.S., Solitary fibrous tumor of the genitourinary tract (2011) AJR Am J Roentgenol, 196, pp. W132-W137Nielsen, G.P., Dickersin, G.R., Provenzal, J.M., Rosenberg, A.E., Lipomatous hemangiopericytoma: A histologic, ultrastructural and immunohistochemical study of a unique variant of hemangiopericytoma (1995) Am J Surg Pathol, 19, pp. 748-756Theunissen, P.H., Ariens, A.T., Pannebakker, M.A., Blaauw, G., Late recurrence of a hemangiopericytoma with lipomatous components (1990) Pathologe, 11, pp. 346-349