Solitary fibrous tumors (SFT) were first described in 1931 (Klemperer P, 1931) as tumors arising from the pleura. The urogenital tract continues to be a rare site but the number of cases reported to date is increasing in the last years, to our knowledge, 20 cases to date. We report two cases of SFT arising in the kidney with benign behavior.CASE 1: 30 year old man, with testicular pain. Grossly, a mass involving almost all kidney and renal capsule (13.5cm diameter). Cut surface of the tumor was firm and tan, with focal yellow haemorrhagic and hyalinized areas. Microscopically, predominant bland spindle-shaped cells with scanty and indistinct cytoplasm and ovoid, vesicular nuclei, showing finely dispersed chromatin, inconspicuous nucleoli without atypia. exhibiting hemangiopericytoma-like pattern, showing stain for Vimentin and CD34, focally for CD99 and bcl-2. CASE 2: 45 year old man asymptomatic. Grossly, a mass in left kidney (7.5 cm diameter). Cut surface was whittish, trabeculated and firm. Microscopicalley, the tumor was well circumscribed and monotonous, composed of bland spindle cells with hyalinized collagenous tissue in a storiform pattern with a prominent vascular component in an hemangiopericytoma-like pattern. The tumor cells had scant cytoplasm, vesicular ovoid nuclei, inconspicuous nucleoli without atypia. Showed stain for Vimentin, CD34 and Bcl-2. DISCUSSION: In general, SFT show blunt histology and a benign clinical course, although 2 cases have had a malignant outcome (Fine S, 2006, Bozkurt SU, 2007). Because the current cases did not fulfill malignancy criteria, such as the presence of necrosis, haemorrhage, high mitotic rate, atypical mitosis or p53 expression, we consider them to be benign SFT of the kidney. Pathologists should be aware of this diagnosis because of the medical boarding of the disease could change drastically.References:1. Klemperer P, Rabin CB. Primary neoplasms of the pleura: a report of five cases. Arch Pathol. 1931;11:385-412.2. Fine S, McCarthy D, Chan T. Malignant solitary fibrous tumor of the kidney. Arch Pathol Lab Med. 2006;130:857-861.3. Bozkurt SU, Ahiskali R, Kaya H. Solitary fibrous tumor of the kidney. Case report. APMIS. 2007; 115: 259-62.