This report presents the fine-needle aspiration biopsy (FNAB) findings of a multicystic renal tumor in a 52-yr-old woman. The aspirate smears contained clusters of cells with large, irregular nuclei and cytoplasmic vacuoles. Subsequent nephrectomy revealed a multicystic nephroma (MCN). Although most common in childhood, MCN should always be considered in the FNAB differential diagnosis of a multicystic renal mass in adult patients. Even in cases where the diagnosis of MCN is considered, it may be difficult to distinguish from cystic renal cell carcinoma on the basis of radiographic and FNAB findings.