To assess whether the outcome of hyperosmolar non-ketotic decompensation has changed in the past 20 years with modern medical management, a retrospective study analysis was performed of all patients presenting with the syndrome to a large teaching hospital during the period 1982 to 1986. Twenty-two patients were identified of whom 68 per cent had no previous history of diabetes mellitus. The immediate mortality rate (within 72 h of presentation) was 36 per cent (eight of 22), the overall mortality rate was 41 per cent (nine of 22) and vascular thromboembolism was common. A comparison was made of the early deaths (n = 8) and survivors (n = 14) in an attempt to identify favourable prognostic factors. The two groups could not be distinguished either by clinical or laboratory variables at presentation nor by treatment regimen; however there was a significant delay in establishing the diagnosis in some of the patients who died. Our results indicate there has been no improvement in the outcome of the hyperosmolar non-ketotic decompensation syndrome in the last two decades and that a high index of suspicion is required to identify patients presenting with this condition.