The case presented here is typical of the localized fibrous mesotheliomas reviewed in the literature. It had a disastrous impact on an otherwise unremarkable pregnancy. There is no discussion in the literature of humeral factors related to localized fibrous mesotheliomas, but the fever, chills, and rheumatoid complaints in some patients may suggest such factors. The presence of the tumor in the already hypercoagulable state of pregnancy may have predisposed this patient to pulmonary emboli. Anticoagulation led to hemorrhage from the thin-walled vascular areas of the tumor. This acute bleeding produced the hypovolemic shock on the third postpartum day, with a cascade of events leading to adult respiratory distress syndrome and the patient's ultimate death. This case underscores the importance of broad differential diagnosis as a continuing challenge in the practice of medicine.