OBJECTIVE: To investigate correlates of body mass index (BMI) and other anthropometric measurements in South Asian, Afro-Caribbean and European women in the UK. SUBJECTS: 291 South Asian, 303 Afro-Caribbean, and 559 European women aged 40 ± 69 y in West London, UK. DESIGN: Cross-sectional survey. MAIN OUTCOME MEASURES: BMI, waist-to-height ratio (WHt), and skinfold thicknesses. RESULTS: Compared with European women, South Asian and Afro-Caribbean women were more like to be obese (odds ratios (OR) 1.83 and 3.01, respectively), but less likely to rate themselves as overweight (BMI-adjusted OR 0.19 and 0.34, respectively). The proportion of women who walked at least 2.5 kmad, excluding activity at work, was lower in South Asians (22%) than in Europeans (44%) or Afro-Caribbeans (40%). Among employed women, the proportion who were active at work was higher in South Asians (63%) and Afro-Caribbeans (70%) than in Europeans (49%). In Europeans, obesity was inversely associated with social class, education, smoking, alcohol intake, and distance walked, and positively associated with time spent watching television. Adjustment for alcohol intake, smoking, education and transport, physical activity explained over 80% of the difference in BMI between South Asians and Europeans, but not the difference between Afro-Caribbeans and Europeans. CONCLUSION: The factor that may be most amenable to intervention in South Asian women is low physical activity outside the workplace. The high prevalence of obesity in Afro-Caribbean women, however, is not accounted for by any behavioural factors measured in this study, and the reasons for high rates of obesity in this group remain to be established.