Two cases of fetal hydrothorax were diagnosed during ultrasound examination in asymptomatic women in the second trimester of pregnancy. One recognized at 19 weeks gestation increased in size. Thoracentesis at 24 weeks followed by continuous drainage for 7 days relieved the condition. The other diagnosed at 15 weeks resolved over the next month without interference. Each pregnancy resulted in a normal term infant. Aspiration of fetal hydrothorax should be performed when the condition appears progressive and is not associated with a major structural abnormality.