Allergic rhinitis is a common cause of nasal obstruction in childhood. This prospective study looked at the effect of passive smoking on nasal obstruction in children with and without allergic rhinitis. Eighty-one children took part. Each child was asked to score his or her degree of nasal obstruction on a visual analogue scale. Exposure to passive smoking was determined subjectively using a parental questionnaire, and objectively by measuring the urinary cotinine/creatinine ratio. Results were tabulated using Microsoft Excel and analysed with SPSS statistical software. Nasal obstruction was significantly worse in children with a positive history of allergic rhinitis (p < 0.05). There was also a trend towards a higher nasal obstruction score in children without allergic rhinitis exposed to passive smoking compared to those who were not so exposed. As would be expected, nasal obstruction is worse in children with allergic rhinitis than in those without. Passive smoking tends to increase the symptom of nasal obstruction in children without allergic rhinitis.