Background: Peritoneal carcinomatosis and ascites are frequent and clinically challenging complications associated with several malignancies such as ovarian cancer. Although ascites is rarely reported in patients with advanced renal cell carcinoma (RCC), its true incidence, particularly in non-clear cell variants, remains poorly defined. Here, we describe the incidence of and clinical characteristics associated with ascites in patients with pRCC. Methods: Patients with metastatic renal cell carcinoma (RCC) seen at the NCI Urologic Oncology Branch were identified in a review of our clinical database. The incidence of radiologically and/or cytologically evident ascites, relevant associated clinical characteristics, and survival were evaluated as was the incidence of ascites in a contemporaneous clear cell RCC (ccRCC) cohort. Results: 241 patients with metastatic RCC were seen between 2002 and 2014, including 109 with pRCC and 125 with ccRCC. Seventeen patients with metastatic pRCC (17/109,15.5%) had evidence of malignant ascites, while only 1/125 pts (0.8%) with ccRCC developed this complication. Median age of PRCC patients with ascites was 45.8 years (range: 26.1 to 76.6 years). Ascites was seen in both patients with type 1 (15.6%, 10/64) and those with type 2 pRCC (15.5%, 7/45). Median time to development of ascites from initial diagnosis of metastatic disease was 16 months (95% CI 7-23 months). Median survival from diagnosis of metastatic disease was 25 months (95% CI 13-41months) in patients with ascites, compared to 20 (95% CI 14-31 months) in those without this complication. (p = 0.59). Conclusions: To our knowledge, this is the largest series evaluating the incidence of and outcome associated with ascites in RCC. Although rare in ccRCC, malignant ascites is a fairly common manifestation of metastatic pRCC. In our cohort, patients with ascites appeared to have outcomes comparable to patients with metastatic pRCC without ascites.