Three cases of airway obstruction in fetuses born at 21, 32 and 40 weeks gestation are reported. The first had laryngeal atresia, cystic dysplastic kidneys, oligohydramnios and immense fluid-filled lungs. The second had upper tracheal agenesis, a tracheo-oesophageal fistula, a cystic dysplastic horseshoe kidney, oligohydramnios and normal-sized lungs. The third had a pin-hole mucosal tract through an otherwise atretic larynx, normal kidneys, no oligohydramnios and normal-sized lungs. Lung weight:body weight ratios, radial alveolar or radial canalicular counts and point-counting of sections of lungs in cases 1 and 2 show that laryngeal or tracheal obstruction may prevent or reduce the pulmonary hypoplasia associated with renal dysplasia, and in cases 2 and 3, that grossly enlarged, hyperplastic lungs may not be seen unless obstruction is complete.