Increasingly, congenital thoracic malformations (CTMs) are diagnosed on antenatal ultrasound, but we lack the evidence to suggest rational management, not least because descriptive terms are used inconsistently. This review describes a simplified clinical classification of CTMs, and contrasts it with pathological descriptions. The age related presentations of CTM are described, together with the differential diagnoses of cystic masses presenting both antenatally and postnatally. Antenatally diagnosed CTMs rarely require intervention before birth; and urgent treatment is only required postnatally if the baby is symptomatic and does not respond to medical management. The asymptomatic baby with an antenatal diagnosis of a CTM presents a management conundrum. Definitive imaging is with high-resolution computed tomography (HRCT), but the optimal timing of imaging is unclear. Whether surgery should be offered to asymptomatic infants is also unclear; in the medium term, 5 % of asymptomatic babies will require surgery for complications of the disease. The most vexed question is malignant change; the risk in the medium term is probably less than 5 %, but we have no way of delineating a high-risk group. Indeed, malignancy has been described even after complete resection of a CTM. The author’s personal management is to advocate surgery in the second year of life for all except for the most trivial CTMs, but many would differ and advocate conservative management. More data are needed if we are to rationalise our approach to these infants.