Background Childhood exposure to second-hand smoking (SHS) represents a major cause of serious health problems. Children exposed to SHS are at an increased risk of serious health problems like sudden infant death syndrome, pneumonia, ear infections and more severe asthma. Studies have shown that SHS exposure is quite common, occurring frequently at home and in the car. A previous study conducted in Portugal (2002) with 12–15-year-olds revealed that 38% of the study children (n  =  1141) were daily or occasionally exposed to SHS due to parents or brothers smoking at home. No information was available for 9–10-year-olds.

Objectives (1) To determine parents’ smoking prevalence; (2) to determine parents’ home smoking prevalence.

Methods An anonymous self-administered structured questionnaire was submitted to 793 students (median age 9.14 years; 48.6% girls, 51.4% boys), enrolled in Portugal’s northern region schools.

Results 15.5% of the mothers and 37.0% of the fathers are daily smokers; 11.6% of the mothers and 25.8% of the fathers are daily or occasional home smokers. Fourteen per cent of children report that at least one of the co-inhabitants (father, mother, brother/sister, other) smoke daily at home and 28.0% report that they smoke occasionally at home.

Conclusions Almost half of the children evaluated are daily or occasionally exposed to SHS, because a high proportion of parents smoke regularly at home. Health professionals, especially paediatricians, should systematically enquire and advise parents about the health risks of SHS and advise them to quit or even forward to a specialised query.