Background and aim: Knowledge of the impact of social determinants driving asthma– chronic obstructive pulmonary disease overlap (ACO) is lacking. Our objective was to identify determinants of incident ACO. Methods: A total of 55,053 adults (50–64 years) enrolled in the Danish Diet, Cancer, and Health cohort (1993–97) was followed in the National Patient Registry for admissions for asthma (DJ45–46) and chronic obstructive pulmonary disease (COPD; DJ40–44) and vital status. Incident ACO was defined as at least one hospital admission for both asthma and COPD (different time points, one after baseline). Detailed case history was obtained at baseline. Cox proportional hazards model was used to examine associations between possible determinants and incident ACO, in terms of hazard ratio (HR) and 95% confidence interval (CI). Results: During follow-up, 561 incident cases of ACO were identified. Age (HR 4.4, 95% CI 3.3–5.9, age group 60–65 years), current smoking (HR 3.6, 95% CI 2.8–4.6), unemployment (HR 1.5, 95% CI 1.2–1.8), and being divorced (HR 1.5, 95% CI 1.2–1.9) determined a higher risk of incident ACO, whereas the opposite was found for leisure-time physical activity (HR 0.7, 95% CI 0.6–0.8) and high educational level (HR 0.7, 95% CI 0.5–0.9). In contrast to ACO, preexisting myocardial infarction (MI; HR 1.5, 95% CI 1.2–1.8) and stroke (HR 1.5, 95% CI 1.2–1.9) were associated with a higher risk of COPD. Conclusion: Incident ACO is to a large extent determined by factors related to lifestyle and socioeconomic status.