The significance of ascites cytology has been controversial as far as the diagnosis and staging of ovarian immature teratoma is concerned. A 22-year-old female presented with pelvic masses. Cytologic findings of the ascites were characterized by the presence of abundant sheets of glia cells with small uniform round nuclei, moderate amount of lace-like cytoplasm and cytoplasmic processes. Moreover, clusters of round cells with hyperchromatic small round nuclei, and scant cytoplasm, resembling neuroblastoma cells, were observed. Small rosette formations were also noted. Microscopic examination showed immature teratoma, grade 2 in the right ovary and gliomatosis peritonei with small foci of immature neuroepithelial elements. The patient underwent postoperative chemotherapy and is alive at 3 months later. Ascites cytology can be useful for diagnosis of gliomatosis peritonei with an immature ovarian teratoma in the clinical context.