The aim of this study was to estimate the prevalence of concurrent diagnoses of asthma/COPD and examine its full spectrum of comorbid disorders in Germany. We used nationwide outpatient claims data comprising diagnoses of all statutory health insurees (40+ years) in 2017 (N = 40,477,745). The ICD-10 codes J44 (COPD) and J45 (asthma) were used to identify patients. The odds of 1,060 comorbid disorders were examined in a case-control study design. Of all insurees, 4,632,295 (11%) were diagnosed with either asthma or COPD. Of them, 43% had asthma only, 44% COPD only and 13% both diseases. The prevalence of concurrent asthma/COPD was 1.5% with a slightly higher estimate among females than males (1.6% vs. 1.4%) and constant increase by age in both sexes. Comorbid disorders were very common among these patients. 31 disorders were associated with a strong effect size (odds ratio > 10), including other respiratory diseases, but also bacterial (e.g., mycobacteria, including tuberculosis) and fungal infections (e.g., sporotrichosis and aspergillosis). Patients with concurrent asthma/COPD suffer from comorbid disorders involving various body systems, which points to the need of a multidisciplinary care approach. Regular screening for common comorbid disorders may result in better clinical course and prognosis as well as improvement of patients' quality of life.