BACKGROUND: Adult-onset asthma and chronic obstructive pulmonary disease (COPD) are heterogeneous diseases caused by complex gene-environment interactions. A functional single nucleotide polymorphism of cadherin-related family member 3 (CDHR3), known as a receptor of rhinovirus-C, is associated with childhood-onset asthma especially in atopic individuals. OBJECTIVE: Here, we identified risk factors for adult-onset asthma and COPD, focusing on the impact of the CDHR3 variant in atopic individuals. METHODS: We conducted a longitudinal, retrospective, observational cohort study of 1523 healthy adults with baseline examinations at Tsukuba Medical Center Hospital in 2008 and retrospectively identified new-onset, physician-diagnosed asthma or COPD from 2009 to 2018. We assessed risk factors by the Cox regression analysis. The impact of CDHR3 variant rs6967330 was also examined in individuals with pre-existing atopy. RESULTS: Over 10 study years, 103 people developed airway diseases (79 asthma and 24 COPD; 52 females, average onset-age 55 years old, range 38-80). Higher body mass index (BMI) and lower forced expiratory volume in one second/forced vital capacity (FEV1 /FVC) ratio were significant risk factors (BMI: HR 1.072 [95% CI 1.005-1.14], P = .034; FEV1 /FVC ratio: HR 1.091 [1.044-1.14], P = .00011). Restriction to atopic individuals saw the A allele at rs6967330 and lower FEV1 /FVC ratio to associate with adult-onset disease (A allele: HR 2.89 [1.57-5.20], P = .00062; FEV1 /FVC ratio: HR 1.10 [1.04-1.17], P = .0010). CONCLUSION AND CLINICAL RELEVANCE: Genetic susceptibility to rhinovirus-C infection in atopic individuals is a risk factor for chronic airway diseases even in later life.