With the goal of improving delirium in cancer patients, quetiapine suppositories were formulated in-hospital and their usefulness was investigated. A retrospective survey of medical records was conducted in 108 patients in whom quetiapine suppositories were used, out of 644 patients admitted to a palliative care ward between April 2011 and October 2014. Patient background information, circumstances of administration, degree of improvement in delirium (evaluation of degree of improvement in hyperactive delirium determined using the Agitation Distress Scale [ADS]), and side effects were investigated. In the overall group, including the quetiapine suppository group and the quetiapine suppository combined with another drug group, a significant decrease in ADS value was confirmed after administration of the suppository (p<0.0001), suggesting that this treatment contributed to improvement in delirium. The side effects were similar to those caused by the oral administration of quetiapine, and issues due to the formulation as a suppository were not observed. In conclusion, it was determined that quetiapine suppositories can be used simply and safely, and it is thought that quetiapine suppositories are useful for delirium in cancer patients.