Sonographic evaluation of 43 pregnant women with diabetes mellitus was performed in the third trimester of gestation for evidence of fetal macrosomia. The width of the soft tissues of the shoulder from the skin surface to the proximal humerus was compared with previously reported measurements for their ability to predict fetal macrosomia. The abdominal circumference and shoulder soft tissue measurements were the best individual predictors of macrosomia, but a combination of an abdominal circumference greater than the 90th percentile for gestational age or a shoulder soft tissue width greater than 12 mm was the best predictor with a sensitivity of 96%, specificity of 89%, and accuracy of 93%. The shoulder soft tissue width should be evaluated for evidence of macrosomia in diabetic pregnancies.