Some marginal blepharitis is related to demodex, but this has not yet been reported in Japan. In this study, patients with severe marginal blepharitis with cylindrical dandruff were studied to examine the number of demodex in their cilia.Ten eyes of 10 patients (7 men and 3 women, mean age: 62.9 +/- 9.0 years) with unilateral marginal blepharitis which had cylindrical dandruff in their cilia were studied. Three cilia which had the most cylindrical dandruff were removed from the eyelids for microscopic examination. After cleaning the eyelid margins for 1 week, the examination was repeated. Scoring of itching and foreign body sensation of the patients was performed both before and after the treatment.Demodex folliculorum was detected in the cilia of 8 out of 10 eyes (80%), and 22 cilia out of 30 with cylindrical dandruff. The average number of demodex/cilia was 1.6 +/- 0.9. In all cases, the number of demodex/cillium decreased significantly with the improvement in symptoms and blepharitis.An Increase in the number of demodex might be the pathogen causing blepharitis with cylindrical dandruff, and cleaning of the eyelid margin is effective as a therapeutic method.