Background: The management of suicidal crisis remains a major issue for clinicians, driving the development of new strategies. Methods: We conducted a randomized controlled trial based on a 7-day add-on positive psychology program: gratitude diary (intervention) versus food diary (control) in adults hospitalized for current suicidal ideation or a suicide attempt. The primary effectiveness outcome was between-group differences for mean change of current psychological pain, between the beginning and the end of the 7-day intervention. We measured between-group differences for mean change of suicidal ideation, hopelessness and optimism, and depression and anxiety between inclusion and after the completion of the 7-day intervention. We compared mean change of current psychological pain, suicidal ideation, and hopelessness and optimism between immediate pre and post daily journal completion. Results: Two hundred and one participants were enrolled and randomized. Between pretherapy and posttherapy: There were no significant between-group differences for mean change of severity and intensity of suicidal ideation and current hopelessness. Between-group difference for mean change of current psychological pain was trending (P = 0.05). Mean change of depression, anxiety, and optimism was significantly higher in the intervention than in the control group. Between immediate pre and post daily journal completion: Between-group differences favored gratitude (vs. food) diary for all outcomes (psychological pain, suicidal ideation, and hopelessness and optimism; P < 10-3 ). Participants found the intervention to be more useful than the food diary. Conclusions: Through gratitude diary appears a very straightforward intervention that could be developed as an adjunctive strategy for suicidal patients.