OBJECTIVE: Clinicians may question whether thoughts of being better off dead are normal consequences of aging or symptoms of depression. We examine whether thoughts of suicide are as strongly linked to depression severity in older adults as they are in other age groups. METHODS: Cross-sectional cohort study. Participants included 509,945 outpatients >18 years old from four large integrated healthcare systems in the Mental Health Research Network who completed 1.2 million Patient Health Questionnaires (PHQ) and had data to calculate Charlson Comorbidity Index scores from 2010 through 2012. The PHQ8 estimated depression severity, while suicidal ideation was measured using the 9th item of the PHQ. Data were abstracted from a Virtual Data Warehouse. RESULTS: In older adult patients, suicidal ideation was strongly associated with depression severity. Older adults who had at least moderately-severe depression (PHQ8 >/=15) were 48 times more likely (95% CI: 42.8-53.8) to report suicidal ideation than those with minimal or mild symptoms of depression (PHQ8 <10) after adjustment for all other variables in the model, including medical comorbidity burden. CONCLUSIONS: Depression severity was by far the strongest predictor of suicidal ideation in older adult patients. Older patients with suicidal ideation should be screened for depression.