Renal carcinoid tumors are exceedingly rare tumors that have been primarily documented as case reports in the literature. In this study, we report a series of 21 renal carcinoid tumors, with emphasis on histopathologic features and clinical outcomes. Patient age ranged from 27 to 78 years (average 52 y). The majority of specimens consisted of radical nephrectomies with or without associated lymph node dissection. Nine tumors were present in the left kidney and 10 were present in the right; location was not available for 2 specimens. No anatomic region of the kidney appeared to be preferentially involved. Twenty tumors were unifocal and ranged in size from 2.6 to 17 cm (average 6.4 cm), and 1 tumor presented as 2 nodules measuring 1 and 2.8 cm. Four patients had a documented history of a horseshoe kidney. Two patients had a history of renal calculi and 1 patient had a history of urothelial carcinoma 8 years prior. Presenting symptoms and clinical findings included back or flank pain (n=6/9), enlarging abdominal mass or fullness (n=2/9), hematuria (n=2/9), and anemia (n=1/9). Twelve patients had concurrent metastases at the time of initial surgery to sites including lymph nodes (n=11/12), liver (n=5/12), bone (n=1/12), and lung (n=1/12). One additional patient developed subsequent metastases to the liver within 6 months of surgery. Examination of the specimens identified carcinoid tumor with a variety of patterns including tightly packed cords and trabeculae with minimal stroma (n=17/21), trabecular growth with prominent stroma (n=4/21), focal solid nests (n=4/21), focal glandlike lumina (n=4/21). The border between tumor and normal kidney was sharply defined in most cases (n=16/21), although focal infiltration was noted in 5/21 cases. Extracapsular extension was documented in 11/21 (52%) cases. Calcifications were present in 5/21 cases. Mitotic activity, measured as mitoses per 10 high-power fields, ranged from 0 to 2 in most cases, with 1 case demonstrating up to 4 mitotic figures per single high-power field. Necrosis was absent in all cases. Immunostains were frequently positive for synaptophysin (n=18/20), chromogranin (n=13/20), Cam5.2 (n=14/16), and vimentin (n=12/15). CK7 was focally positive in a small subset of cases (n=3/18) and CK20 was positive in 1 case. TTF-1 and WT-1 were negative in all cases examined. Clinical follow-up was available on 15 patients and ranged from 3 months to 11 years. One patient died of disease at 8 months after surgery and 1 patient died without disease at 11 years after surgery. Of the remaining patients, 7 patients were alive without disease and 6 patients were alive with disease. Additional metastases developed in 4 patients and included metastases to the liver and bone.