Objective To analyze the imaging and histopathologic characteristics of PWS patients with facial hyperplasia, in order to improve the therapeutic effect of the disease. Methods Thirty-two patients with facial hyperplasia treated by laser was retrospected. The degree of hyperplasia and the density of enhanced signals on T1-weighted MRI were graded using quartile scale. The pathological data of 18 cases was retrospectively analyzed and compared with 15 PWS patients without facial hyperplasia, to explore the histological difference. Results MRI results showed statistically significant correlation between the degree of hypertrophy and the density of enhanced signals (P<0.001). Histological features showed that vascular malformation existed not only in the dermis but also in the subcutaneous fat and muscle with much larger vessel diameters(0.048 mm vs 0.020 mm,P=0.004;0.035 mm vs 0.017 mm,P=0.008)and thicker vessel walls(0.014 mm vs 0.006 mm, P=0.003;0.010 mm vs 0.006 mm,P=0.020). Conclusion The involvement of the subcutaneous tissue by CM, which exceeds the damage depth of laser for blood vessels,might be one of the major cause of poor therapeutic effect with laser therapy.