Over a 1-year period, 28 patients (13.6% of admissions to one surgical intensive care unit) developed the new onset of a supraventricular tachyarrhythmia requiring treatment. None was associated with intravascular catheter placement. There were 16 women and 12 men with an average age of 69.8 years (range 49-92). In nine of the patients, the diagnosis was made coincidental with or immediately before the onset of postoperative sepsis. Twenty-six patients responded to medication and two required cardioversion. Mortality was 28.6 per cent (8/28), but none as a direct result of the arrhythmia. One patient had a myocardial infarction secondary to the arrhythmia. Supraventricular tachyarrhythmias are a relatively common problem in the critically ill surgical patient. Surgeons who care for such individuals need to be familiar with the differential diagnosis and treatment of arrhythmias. The new onset of a supraventricular tachyarrhythmia in an otherwise stable patient should prompt a search for a treatable cause of sepsis.