Background. Gastrointestinal stromal tumors (GISTs) are the most common mesenchymal tumors of the digestive tract and are diagnosed relatively seldom in pregnancy. Case. We describe a remarkable clinical course and long-term outcome, now nine years after first diagnosis, of a massive and metastatic, with a high malignancy grade GIST case, found in and treated from the first trimester of pregnancy onwards. Conclusion. GIST occurring during pregnancy is extremely rare. However, early diagnosis is important for optimal management. The recent better understanding of oncogenesis, the use of immunohistochemistry for differential diagnosis of GISTs, and the use of imatinib mesylate as the treatment of first choice are-as shown in this case-important for care of pregnant women with this type of malignancy.