Obesity is known to increase maternal morbidity and mortality. We describe a case of obstructive sleep apnea due to obesity and discuss our treatment of the resulting pulmonary hypertension. A patient was transferred to our hospital at 29 weeks' gestation with severe anasarca and more than a 100-pound weight gain during pregnancy. Pulmonary hypertension due to obstructive sleep apnea was diagnosed. The patient was treated with nasal continuous positive airway pressure (CPAP) during sleep and remained in the hospital the remainder of her pregnancy. She had a massive spontaneous diuresis during her hospital stay and lost more than 100 pounds. She was delivered at term via cesarean section because of transverse lie. Preoperative hemodynamic monitoring confirmed the diagnosis of pulmonary hypertension. This represents the first case in the literature of obstructive sleep apnea leading to pulmonary hypertension in pregnancy. This patient responded well to nasal CPAP as evident by the massive diuresis and good maternal outcome.