Many psychiatric and somatic comorbidities increase the risk of suicidal behavior, but the effect of co-existing comorbidities is sparsely elucidated. We described co-existence of psychiatric and somatic comorbidities and the influence of the combined comorbidity burden on the risk of suicidal behavior.

We defined two case populations above 10 years in the Danish health registries: those who 1) died by suicide (2010–2020) and 2) had an incident suicide attempt (2010–2021). Co-existing somatic and psychiatric comorbidities and relative odds of suicidal behavior at increasing comorbidity burden were assessed.

Among 5.9 million Danish citizens (2021), 6,257 individuals died by suicide whereas 30,570 had an incident suicide attempt. More than half had ≥2 co-existing psychiatric and/or somatic comorbidities. Of those who died by suicide, 18% had co-existing mood disorders and stress disorders, while 5% had both mood disorders and cancer. An 88-fold increase of odds for attempting suicide and a 35-fold increase of odds for suicide were observed among those with the highest combined burden of somatic and psychiatric comorbidities relative to those without. The presence of somatic comorbidities seemed to protect against suicide in older individuals.

Psychiatric and somatic comorbidities commonly co-exist in individuals with suicidal behavior. Higher combined burden of psychiatric and somatic comorbidities increased the odds of suicidal behavior, though the presence of somatic diseases had a potential protective effect on the risk of suicide in older individuals. This warrants collaboration and enhanced awareness of suicidal behavior risks across somatic and psychiatric departments.