Elevated rates of premature mortality are recorded for persons with noncommunicable diseases. Researchers aimed at determining the contribution of psychiatric comorbidity by ascertaining the risks of premature mortality and suicide in people with common noncommunicable diseases, with and without psychiatric disorder comorbidity.

• Over 1 million patients born between 1932 and 1995 and diagnosed with chronic respiratory diseases, cardiovascular diseases, and diabetes were investigated using national registers in Sweden.

• Death of more than 7% of the patients occurred by any cause within 5 years; 0.3% died from suicide.

• Patients with psychiatric comorbidities had more than double of these risks compared with those without such comorbidities.

• Identification and diagnosis of most of the psychiatric comorbidities were made before the noncommunicable diseases.

• Familial risk factors that were shared between the siblings (e.g., genetic and childhood environmental risk factors) were accounted for by comparing each of the patients with their unaffected siblings.

• In the sibling comparison analyses, psychiatric comorbidity was noted to be consistently linked with increased rates of premature mortality and suicide and the associations persisted following additional adjustments for sociodemographic factors and body mass index (BMI).

• Overall findings suggest that in people admitted to general hospitals for chronic health conditions, identification and treatment of co-occurring substance use disorders and depression may lower mortality and morbidity in these patients.