A 43-year-old full-term pregnant woman (gravida 2, para 1, medical history of gestational diabetes mellitus) developed a sudden and malignant hypertension with hemoptysis, sweat, and tachycardia during a scheduled C-section. A dead newborn was delivered and was successfully resuscitated. The mother died after resistant cardiac arrest. Autopsy and pathological analyses revealed an acute pulmonary edema and a necrotic and hemorrhagic voluminous tumor of the left adrenal gland, which was a pheochromocytoma. Pheochromocytoma is a rare tumor of the adrenal glands which secretes catecholamines. In pregnant women, its symptoms can mimic gestational hypertension, preeclampsia or eclampsia, and gestational diabetes mellitus. The gestational diabetes mellitus was presumed to be a symptom of the pheochromocytoma, and cardiopulmonary failure the result from the necrosis of the tumor provoked by gravid uterus compression. From a medico-legal point of view, the tumor could not have been suspected during the pregnancy.