Few studies have examined the contribution of life-course factors in explaining familial aggregation of chronic lung conditions. Using data from the 1958 British Birth Cohort, a life-course approach was used to examine whether, and how, exposure to risk factors through one's life explained the association between parental respiratory disease history and symptomatic airflow obstruction (AO). Cohort participants (n=6212) were characterised in terms of parental respiratory disease history and symptomatic AO at 45 years. Life-course factors ( smoking, asthma and early-life factors) were operationalised as life period-specific and cumulative measures. Logistic regression and path analytic models predicting symptomatic AO adjusted for parental respiratory disease history were used to test different life-course models (critical period, accumulation- and chain-of-risks models). While some life-course factors ( childhood passive smoking and occupational exposure) were individually associated with parental respiratory disease history and symptomatic AO, asthma (OR 6.44, 95% CI 5.01-8.27) and persistent smoking in adulthood (OR 5.42, 95% CI 4.19-7.01) had greater impact on the association between parental respiratory disease history and symptomatic AO. A critical period model provided a better model fit compared with an accumulation-of-risk model and explained 57% of the effect of parental respiratory disease history on symptomatic AO. Adulthood asthma and smoking status explained around half of the effect of parental respiratory disease history on chronic obstructive pulmonary disease. Beyond smoking history, the combination of parental respiratory disease history and adulthood asthma may provide an opportunity for early diagnosis and intervention.