Abstract： Objective To analyze the histologic characteristics of macrochilia secondary to portwine stain and to elucidate the possible mechanism.Methods Twenty-one cases of macrochilia secondary to venular malformation were included and the histology of the lesions was observed by light microscope.Results Histological examination revealed vascular abnormalities and a number of widely distributed hamartomatous changes in macrochilia secondary to venular malformation.The average vessel diameter is (39.8±15.7)μm.The degree of hamartomatous change:mild(1 case),moderate(7 cases)and severe(13 cases).Conclusions The complex hamartomatous changes suggest a genetically determined,multilineage developmental field defect in the pathogenesis of venular malformation.