Previous studies have suggested that South Asian (SA) ethnicity is a predictor of poorer outcome after coronary artery bypass grafting (CABG). Our aim was to identify potential reasons for the higher postoperative mortality in SA patients and investigate all these reasons. All individuals undergoing isolated CABG in a tertiary cardiac centre from April 2002 to September 2007. In total, there were 2897 subjects (2623 white subjects; 274 SA subjects) who were included in an observational study showing the effect of ethnicity on the medium-term survival following CABG. Survival at 30 days and survival up to five years (median 2.7 years) were measured. SA subjects undergoing CABG were younger (62+/-9 vs. 66+/-9 years, P<0.001), less obese [body mass index (BMI) 26+/-4 vs. 28+/-4 kg/m(2), P<0.001] and had a higher prevalence of diabetes mellitus (58% vs. 33%, P<0.001) compared with white subjects. Thirty-day mortality was higher in SA subjects (2.6% vs. 1.0%, P=0.02). Non-diabetic SA had similar 30-day mortality, five-year survival and life expectancy compared to non-diabetic white subjects. In contrast, diabetic SA had a higher 30-day mortality (3.8% vs. 1.4%, P=0.01) and worse life expectancy compared to diabetic white subjects. The higher early postoperative mortality observed in SA patients is related to higher incidence of diabetes among them. SA diabetics have a significantly higher postoperative mortality and worse overall life expectancy. Ethnicity per se is not an independent predictor of short- or medium-term survival after CABG.