Gynecologic cancer in patients with subacute cerebellar degeneration predicted by anti-Purkinje cell antibodies and limited in metastatic volume. Between 1982 and 1989, 19 patients with gynecologic carcinoma, paraneoplastic cerebellar degeneration, and seropositivity for anti-Purkinje cell cytoplasmic antibodies were identified at our institution. Seven of the patients had no clinical, computed tomographic, or magnetic resonance imaging evidence of cancer but had undergone laparotomy solely because anti-Purkinje cell antibodies were found in their serum; all had high-grade adenocarcinoma. Cerebellar symptoms preceded or coincided with the initial cancer diagnosis in 15 patients and preceded the diagnosis of recurrent cancer in 4 patients. The cancers were 14 ovarian, 2 fallopian tube, 2 surface papillary, and 1 poorly differentiated metastatic adenocarcinoma in a periaortic lymph node. Two remarkable surgical observations in patients with high-grade ovarian and tubal cancers were the conspicuous lack of peritoneal implants and the small metastatic volume. A comparison of the 8 patients who had primary stage III cancer with 24 matched control patients without paraneoplastic cerebellar degeneration revealed no difference in primary tumor volume but a significantly smaller volume of metastatic tumor in the seropositive group (P = 0.05). Anti-Purkinje cell antibodies were not detected in 111 neurologically normal patients with advanced ovarian cancer. The small metastatic volume in the face of high-grade and advanced stage malignancy in seropositive patients with paraneoplastic cerebellar degeneration suggests that an immune response to the tumor (presumably cross-reactive with cerebellar cells) may impair the metastatic process. Earlier diagnosis and treatment of cancer, based on prompt serologic testing, may offer an improved neurologic and oncologic prognosis. 