OBJECTIVE To determine if an adverse relationship exists between passive smoking and respiratory function in very low birthweight (VLBW) children at 11 years of age. METHODS The Royal Women's Hospital, Melbourne. METHODS 154 consecutive surviving children of less than 1501 g birthweight born during the 18 months from 1 October 1980. METHODS Respiratory function of 120 of the 154 children (77.9%) at 11 years of age was measured. Exposure to passive smoking was established by history; no children were known to be actively smoking. The relationships between various respiratory function variables and the estimated number of cigarettes smoked by household members per day were analysed by linear regression. RESULTS Most respiratory function variables reflecting airflow were significantly diminished with increasing exposure to passive smoking. In addition, variables indicative of air-trapping rose significantly with increasing exposure to passive smoking. CONCLUSIONS Passive smoking is associated with adverse respiratory function in surviving VLBW children 11 years of age. Continued exposure to passive smoking, or active smoking, beyond 11 years may lead to further deterioration in respiratory function in these children.