Extraskeletal Ewing's sarcoma (EES) is a round-cell malignancy that manifests most commonly in the paravertebral and intercostal regions. It occurs predominantly in adolescents and young adults, between the ages of 10 and 30 yr, and follows an aggressive course with a high recurrence rate. Distant metastasis is also common. The tumor is often confused with other round, small-cell neoplasms, including primitive neuroectodermal tumor, neuroblastoma, embryonal rhabdomyosarcoma, and lymphoma. This report pertains to a fine-needle aspiration cytologic diagnosis of EES, supported by clinicopathologic and fine structural correlations in a 56-yr-old man who presented with a rapidly growing, massive, right groin mass. The smears showed a diffuse cellular population of malignant round cells composed of two types: one group of larger cell exhibiting a thin-rim, pale cytoplasm, less hyperchromatic nuclei, nucleoli, and diffusely dispersed chromatinic nuclear details; and the second group of smaller and darker cells with highly hyperchromatic and almost smudged nuclei. These are chief cells and dark cells, respectively. Special studies revealed significant intracytoplasmic glycogen and positive vimentin and HBA-71 immunostaining. Cytogenetic findings of chromosomal 11;22 translocation is also supportive of the diagnosis of EES.