The objective of the study was to determine the clinical characteristics and mortality of patients with hyperglycaemic hyperosmolar syndrome (HHS) and diabetic ketoacidosis (DKA) at a Jamaican tertiary care hospital. In a retrospective study of 1560 admissions for diabetes during the period 1998-2002, 980 dockets were reviewed and 164 individuals met the ADA diagnostic criteria for DKA or HHS. Patients with HHS were older than DKA patients (64.5 years [95% CI: 60.7-68.4] versus 35.9 years [95% CI: 30.2-41.6]), but were not more likely to be non-compliant with medications, infected, or male. Overall, 24% had a mixed DKA/HHS syndrome. Most DKA patients had type 2 diabetes (62%). Only 2% of HHS and 6% of DKA/HHS patients had type 1 diabetes. Syndrome specific mortality was: DKA 6.7%, HHS 20.3%, and DKA/HHS 25% (p for trend=0.013). Mortality increased significantly with age, especially in patients > or =50 years. Significant univariate predictors of mortality were altered mental status on admission, co-existing medical disease, increasing age, older age at onset of diabetes, acute stressors, and DKA/HHS. In multivariate models, only altered mental status was significant (OR=3.59; 95% CI: 1.24-10.41). Hence, hyperglycaemic crises in a Jamaican tertiary care hospital are associated with significant mortality especially in patients who are older or with altered mental status.