Fukunaga M. Neuron-specific enolase-producing leiomyosarcoma of the mesentery. Case report. APMIS 2004;112:105–8. A case of neuron-specific enolase (NSE)-producing leiomyosarcoma arising in the mesentery of a 62-year-old female is presented. Preoperatively, serum level of NSE was markedly elevated. A well-defined but unencapsulated tumor measuring 14×12×9 cm was histologically characterized by a fascicular or herring-bone arrangement of atypical spindle or oval tumor cells with vesicular cigar-shaped nuclei, inconspicuous nucleoli and abundant clear to brightly eosinophilic cytoplasm. Immunohistochemically, the tumor was positive for vimentin, α-smooth muscle actin, muscle actin, desmin, and γ-NSE. Postoperatively, serum level of NSE decreased to within normal range. The NSE levels were, however, elevated again as metastatic lesions in the liver had enlarged. The patient died of the liver metastases 10 months after surgery. Serum NSE level can be a useful index of tumor extent and for monitoring treatment of some patients with leiomyosarcoma.