Congenital lung lesions are common sonographic findings in pregnancy, usually detected at the routine 20 weeks scan. The most common is cystic adenomatous malformation of the lung (CCAM). This usually causes few prenatal problems; however, fetal hydrops occurs in about 5%. Prenatal intervention for these is possible in many to allow survival to birth. Bronchoplumonary sequestration (BPS), with an aberrant "feeder" vessel arising from the aorta may co-exist but is detectable as a separate entity by visualization of this vessel. Symptomatic or curative prenatal intervention is again possible in the few severe cases where hydrops or pleural effusions develop. Pleural effusions may be due to a primary leak usually of chylous fluid: prenatal thoracoamniotic shunting may prevent pulmonary hyoplasia or cure the consequent fetal hydrops. More often, however, effusions are a consequence of an underlying abnormality, including many structural or chromosomal abnormalities that may also cause co-existing fetal hydrops. Congenital high airway obstruction (CHAOS) is commonly fatal but cases potentially amenable to prenatal intervention or to immediate perinatal management may be identified using ultrasound or MRI.