Delirium complicates pain assessment and management in advanced cancer. This retrospective cohort study compared health-care workers’ (HCWs) cancer pain judgments between older patients with advanced cancer with and without a diagnosis of delirium. We reviewed HCWs’ daily chart notations about pain presence and good pain control in 149 inpatients with advanced cancer, ≥65 years of age, admitted to a palliative care inpatient unit. Any day with 1 or more notations of pain presence was counted as 1 day with pain; days with notation(s) indicating good pain control were similarly counted. Proportions of days that HCWs judged inpatients to have pain and good pain control were calculated. Patients with and without a delirium diagnosis were compared on both pain outcomes. The moderating effect of highest analgesic class administered was examined. Although most patients received opioid analgesics, mean proportions of days with judged pain were high (39%-60%) and mean proportions of days with judged good pain control were low (<25%) across groups. Among patients receiving either opioid or nonopioid medication, patients with delirium demonstrated lower proportions of days with judged good pain control than patients without delirium (P ≤ .001), even though groups did not differ in proportions of days with judged pain (P = .62). Cancer pain is difficult to manage in advanced cancer, especially when delirium is present; however, misinterpretation of delirium symptoms as pain cues may inflate pain judgments. Findings require replication but suggest the need for better pain assessment in older patients with advanced cancer and delirium.