A longitudinal cohort study from New Zealand has suggested a unidirectional cause and effect relationship between cigarette smoking and depression, in which smoking increases the risk of developing symptoms of depression. The Christchurch Health and Development Study has followed up a group of 1,265 children who were born in 1977. Participants were studied at ages 18, 21 and 25, when 79-81% of the original cohort attended. 'When case finding among patients with chronic conditions, smoking is yet another important risk factor to add to the list of functional impairment, previous depression, physical inactivity, obesity and maladjustment. More controversially, it has been suggested that we should routinely target smoking cessation when treating depressed smokers.'