We describe the case of an 18-year-old girl with an oligodendroglioma arising in an immature ovarian teratoma. The oligodendroglioma, which closely involved the cystic teratoma, was moderately cellular, composed of monomorphic cells with uniform round nuclei and perinuclear halos with a characteristic "fried-egg" appearance. Rare microcalcifications and a dense network of branching capillaries with a chicken-wire appearance were also observed. By immunohistochemistry, tumour cells showed positivity for S-100, but were negative for GFAP, synaptophysin and neuro-specific enolase. The patient is free of disease on follow-up examination at 24 months.