Massive ovarian edema is a tumor-like condition occurring in young women considered to be the result of torsion of the ovary to the extent that it interferes with venous and lymphatic drainage, but is insufficient to cause necrosis. Marked enlargement of the ovary occurs, and the patient usually presents with an adnexal mass. If the torsion occurs acutely abdominal pain is prominent. If it occurs gradually, the patient may be virili/ed and stromal luteini/ation is often observed microscopically within the involved ovary. Edema fluid accumulates in the stroma but the tunica albuginea and superficial cortical zone are characteristically uninvolved. In one patient, precocious puberty was the presenting finding and this regressed following excision of the mass. This unique finding suggests that the lesion can result in the production of significant quantities of estrogen, and that this is less likely to be recognized after menarche. In the case studied by electron microscopy, the principal finding was the presence of both fibroblasts and myofibroblasts in the edematous stroma. The increased number of myofibroblasts may be a response to the edema.