A 67-year-old woman underwent resection of a gastric tumor and a synchronous metastatic lesion of the liver in 1991. Histopathologically, both the primary and metastatic tumors were diagnosed as leiomyosarcoma. Four years after the initial resection, another liver metastasis was detected in the caudate lobe, and a partial hepatectomy was performed. Multiple bilateral lung metastases were identified 7 years later and one was resected. Immunohistochemically, tissues from both the primary and metastatic sites were positive for KIT and CD34, and a c-kit gene mutation was found in the resected lung lesion. The remaining lung metastases responded to treatment with imatinib mesylate, but the treatment was discontinued because of toxicity. The patient remains under observation and the lung lesions have not progressed. At present she has no symptoms, and she has had no further recurrences in the past 3 years. This case is extremely unusual; a slowly progressing gastrointestinal stromal tumor over the course of 17 years from the initial diagnosis, with hematogenous metastases at multiple sites.