The cytologic findings of endodermal sinus tumor of the ovary are reported. The cytologic preperations were obtained from ascitic specimens. The findings on Papanicolaou-stained smears included a clean background and poorly preserved atypical cells loosely arranged in irregular or papillary groups. At high magnification, the cells had ill-defined and microvacuolated cytoplasms, with an increased nuclear-cytoplasmic ratio and prominent nucleoli. Hyaline globules characteristic of the alpha-fetoprotein (AFP)-synthesizing cells of endodermal sinus tumor were observed within the cells with periodic-acid-Schiff(PAS) stain. The presence of PAS-positive hyaline globules can be regarded, therefore, as a diagnostic clue to endodermal sinus tumor in an appropriate clinical setting and in the presence of AFP production. The cytologic findings in a cell block is important, in addition to smears, to obtain more diagnostic clues. A preliminary cytomorphologic diagnosis of this highly malignant tumor is valuable as a guide in planning further immunocytochemical and serologic studies.