Suicidal ideation, or suicidal thoughts, is the thought process of having ideas, or ruminations about the possibility of ending one's own life. It is not a diagnosis but is a symptom of some mental disorders and can also occur in response to adverse events without the presence of a mental disorder.

On suicide risk scales, the range of suicidal ideation varies from fleeting thoughts to detailed planning. Passive suicidal ideation is thinking about not wanting to live or imagining being dead. Active suicidal ideation involves preparation to commit suicide or forming a plan to do so.

Most people who have suicidal thoughts do not go on to make suicide attempts, but suicidal thoughts are considered a risk factor. During 2008–09, an estimated 8.3 million adults aged 18 and over in the United States, or 3.7% of the adult U.S. population, reported having suicidal thoughts in the previous year, while an estimated 2.2 million reported having made suicide plans in the previous year. In 2019, 12 million U.S. adults seriously thought about suicide, 3.5 million planned a suicide attempt, 1.4 million attempted suicide, and more than 47,500 died by suicide. Suicidal thoughts are also common among teenagers.

Suicidal ideation is associated with depression and other mood disorders; however, many other mental disorders, life events and family events can increase the risk of suicidal ideation. Mental health researchers indicate that healthcare systems should provide treatment for individuals with suicidal ideation, regardless of diagnosis, because of the risk for suicidal acts and repeated problems associated with suicidal thoughts. There are a number of treatment options for people who experience suicidal ideation.