Background: For patients with suicide attempts or self-harm, acute-care hospitals often function as the primary or sole point of contact with the healthcare system. However, little is known about patient characteristics or clinical trajectories of suicide attempts and self-harm episodes among those admitted to acute-care hospitals. This study aimed to describe the characteristics of suicide attempts and self-harm among patients admitted to acute-care hospitals, and the clinical practices provided in these hospitals, using a nationwide inpatient database in Japan. Methods: Using data from the Japanese Diagnosis Procedure Combination inpatient database from June 2015 to March 2017, we identified patients with emergency admission for suicide attempts or self-harm. We did not include patients with elective admission to psychiatric hospitals or outpatients. We described patient characteristics, treatments for physical injuries, psychiatric interventions, and discharge status. Results: We identified 17,881 eligible patients during the 22-month study period. Overall, 38% of the patients did not have any psychiatric or behavioral comorbidities at admission. The most common suicide method was drug overdose (50%), followed by hanging (18%), jumping from a height (13%), cutting or piercing without wrist cutting (7.1%), poisoning (6.6%), and wrist cutting (5.4%). Suicide was completed by 2,639 (15%) patients. Among patients discharged to home, 51% did not receive any psychiatric intervention. In 468 acute-care hospitals (54%), no psychiatric intervention was provided during the study period. Conclusion: We found that half of acute-care hospitals did not provide any hospital-based psychiatric care for patients with suicide attempts or self-harm.