Abstract The aim of this study was to determine the risk of adverse events for risperidone and haloperidol in delirium patients. The authors conducted a retrospective study with medical records of 266 Japanese delirium inpatients who were referred to them between July 2001 and May 2005. Information on gender, age, delirium, drug therapy, adverse events, death, and other relevant factors was collected and analyzed for each patient. As a primary antipsychotic drug for the treatment of delirium, risperidone was used in 93 patients; oral haloperidol was used in 95; and intravenous or intramuscular haloperidol was used in 61. The incidence of adverse events was 6.5% for risperidone, 31.4% for oral haloperidol, and 32.8% for haloperidol injection. The incidence of death during delirium was 3.2% for risperidone, 2.1% for oral haloperidol, and 13.1% for haloperidol injection. The incidence of death within 1 year after the onset of delirium was 30.1% for risperidone, 29.5% for oral haloperidol, and 45.9% for haloperidol injection. Between risperidone, oral haloperidol, and intravenous or intramuscular haloperidol the incidence of adverse events was significantly lowest for risperidone, and the incidence of death during delirium was significantly highest for intravenous or intramuscular haloperidol. The use of haloperidol as a first-line drug in delirium patients who can receive the drug orally will not contribute to the establishment of drug therapy for delirium based on risk-benefit assessment of the therapy.