A follow-up study on 82 patients with congenital choanal atresia revealed that the malformation was twice as common in females as in males and occurred on the right side only in 56% of the cases. The family histories, however, revealed no obvious hereditary trend, and a chromosome analysis showed no abnormalities. Additional malformations were observed in 49% of the patients, but with no constant pattern substantiating a syndrome. The findings of the present study indicate that the atresia may result from a persisting bucconasal membrane. In about 50% of the patients the nasal cavity was funnel-shaped with a posterior narrow end, but the height of the palatal vault did not differ from the normal. The frequency of otitis media and sinusitis was high, 31% and 21% respectively.