Effusions, especially peritoneal, are seen in less than 2% of patients with renal cell carcinoma (RCC). Since the tumor cells in RCC are bland and nondescript, the involvement of serous effusions is difficult to diagnose. An accurate recognition of malignant effusion and differentiation from reactive mesothelial cells is imperative. A 55-year-old male presented with gradually progressive ascites. Cytospin preparations from ascitic fluid showed reactive mesothelial cells admixed with few smooth-contoured clusters of cells with moderate cytoplasm, vesicular nuclei with prominent nucleolus. He had undergone nephrectomy for papillary RCC two years earlier. Another 36-year-old man underwent left nephrectomy for suspected RCC. Intra-operative ascitic fluid was sent for cytologic examination and showed numerous reactive mesothelial cells along with few clusters of cells with scant to moderate amount of cytoplasm, vesicular nucleus and a small nucleolus. Considering the histomorphology of the primary renal tumor in both cases, a cytologic diagnosis of malignant peritoneal effusion, morphologically compatible with RCC was rendered. RCC, due to its bland cytologic features, is easily overlooked in effusions. In a known patient, the cytopathologist must be extra vigilant to pick up the few cell clusters present in the fluid preparations and differentiate them from reactive mesothelial cells. A close inspection of the cytologic features and comparison with the histopathology of the primary tumor helps in making an accurate diagnosis.