AbstractBackgroundChildhood asthma is a common condition whose prevalence is changing. We hypothesized that the relationship between asthma and associated risk factors has changed over a 50‐year period.MethodsAn ecological study design was used. Children aged 8–13 attending schools in Aberdeen city were surveyed on seven occasions between 1964 and 2014. The following were determined: history of asthma, history of eczema, parental smoking, parental asthma, sex and socio‐economic status. Analysis was by a structural change model with two knots. The outcome reported was the change in odds ratio between asthma and a given risk factor during a given period.ResultsThere were 23,241 questionnaires distributed and 17,439 returned (75%). The odds ratio (OR) for a child with asthma to have eczema increased between 1989 and 1999 by 1.031 [95% CI 1.028, 1.035] and by 1.042 between 2004 and 2014 [1.038, 1.047]. The OR for a child with asthma to have a parent who smoked rose by 1.032 [1.028, 1.036] between 1989 and 1999 and by 1.043 [1.038, 1.047] between 2004 and 2014), and to have a parent with asthma (1.027 [1.022, 1.031] for 1994–99 and 1.042 [1.037, 1.048] for 2004–2014). The OR for a child with asthma being male, but not and being from the most deprived communities, rose between 1989–1999 and 2004–2014.ConclusionsThe relationship between asthma prevalence and particular risk factors changed over the 50‐year period of study, and this might reflect changes in children's environment and/or susceptibility.