Doctors say hospitalised children often live in harmful housing conditions and are calling for a warrant of fitness for all rental houses.
A study of children admitted to Wellington hospital last winter found half of the children lived in cold houses, a third in damp houses and a quarter in houses that had mould in their living areas.
Michael Baker from the University of Otago led the study and said the health of children living in those conditions is constantly undermined, leading to repeated hospital visits.
Parents and caregivers of 106 children were interviewed over a period of two weeks in winter 2012.
Dr Baker said it was the first time a large number of parents whose children are in hospital have been interviewed about their housing conditions.
The study also found 38% of the children were exposed to second-hand smoke.
A warrant of fitness for rental housing was a recommendation in a recent report of the Children's Commissioner's expert working group on solutions to child poverty.