Background In older people, chronicity is associated with delirium, which in turn increases the risk of developing poor clinical outcomes like nursing home admission and death. The aim is to determine whether chronicity, as assessed by Clinical Risk Groups (CRG), is an independent predictor of mortality in older adults with delirium seen in the emergency department (ED). Methods Prospective study with 18-month follow-up. Included patients were aged 65 years or older, admitted from 1 January to 31 December 2020, and diagnosed and coded for delirium in the ED of a secondary hospital. Patients were followed for 18 months. A survival analysis was performed using the Kaplan-Meier method and a multivariate Cox proportional hazards model. Results The study included 125 patients (56 % men, mean age 81.2 years, standard deviation [SD] 7.5). At baseline, level 0 chronicity was present in 4.7 % of the patients; level 1, 23.4 %; level 2, 32.8 %; and level 3, 39.1 %. By study end, 29.68 % (n = 38) had died. Mean survival in the total sample was 176.6 (standard error 25.8) days. Level 3 chronicity was associated with a significantly higher risk of mortality (hazard ratio 3.41, 95 % confidence interval 1.31–8.96). Conclusions Level 3 chronicity, as assessed by Clinical Risk Groups, is an independent predictor of mortality in older ED patients with delirium. Delirium leads to an increased level of chronicity over the following months.