To investigate the association between socioeconomic status (SES) and outcomes for seriously ill patients.

A retrospective cohort study based on data from an intensive care unit clinical database linked with data from the Western Australian hospital morbidity and mortality databases over a 16-year period (1987–2002).

In-hospital and long-term mortality.

Data on 15 619 seriously ill patients were analysed. The in-hospital mortality rate for all seriously ill patients was 14.8%, and the incidence of death after critical illness was 7.4 per 100 person-years (4.8 per 100 person-years after hospital discharge). Patients from the most socioeconomically disadvantaged areas were more likely to be younger, to be Indigenous, to live in a remote area, to be admitted non-electively, and to have more severe acute disease and comorbidities. SES was not significantly associated with in-hospital mortality, but long-term mortality was significantly higher in patients from the lowest SES group than in those from the highest SES group, after adjusting for age, ethnicity, comorbidities, severity of acute illness, and geographical accessibility to essential services (hazard ratio for death in lowest SES group v highest SES group was 1.21 [95% CI, 1.04–1.41]; P = 0.014). The attributable incidence of death after hospital discharge between patients from the lowest and highest SES groups was 1.0 per 100 person-years (95% CI, 0.3–1.6 per 100 person-years).

Lower SES was associated with worse long-term survival after critical illness over and above the background effects of age, acuity of acute illness, comorbidities, Indigenous status and geographical access to essential services.