Tuberculosis (TB) continues to cause significant morbidity and mortality worldwide, even in resource-rich, TB low-incidence settings like Denmark. Only few studies evaluate the risk of TB in relation to mental illness. Interestingly, the risk may be higher due to underlying mechanisms both epidemiologically and through immunological pathways as recently pointed out by Dai et al.1 A recent systematic review concluded that mental health was an important risk factor for active TB globally, however none of the 10 studies included in the final analysis were European or from the United States.2 To obtain more knowledge from a resource-rich, TB low-incidence setting, we conducted a nationwide case-control study in Denmark spanning three decades analysing the impact of comorbidities on TB risk with a special focus on mental illness. Cases were all TB patients ≥ 18 years of age notified with TB to the national TB Surveillance Registry between 1 January 1990 and 31 December 2018 (n = 9581) in Denmark. Controls were matched (1 case: 3 controls) on sex and date of birth. The unique Danish central person registration (CPR) number given at birth or immigration into the country was used to track and link information at an individual level through the nationwide registries. From this database, a study on social risk factors and TB has previously been published.