Background : Inverted follicular keratosis has distinctive histopathological features and is infre quently encountered by dermatologists. To date, the pathogenesis of inverted follicular keratosis has not, been concluded. Many authors have suggest,ed several theories for the nature of invert.ed follicular keratosis including vearuca vulgaris with squamous eddies, irritated seborrheic keratosis and dist,inctive follicular tumors. Objective : It is the purpose of this study to observe and compare the clinical features of in verted follicular keratosis with previous studies and evaluate the possible relationship between in verted follicular keratosis and human papillomavirus to clarify the nature of this condition. Methods : We studied 9 patients with inverted follicular keratosis for clinical features including the duratiori of the disease, the location and size of the lesions, the clinical impressions at the first visit and we made a record of the patients age and sex. To evaluate the relationship be tween inverted follicular kerato is and the human papillomavirus, we performed immunohistochvm ical staining using polyclonal antibodies to the human papillomavirus common antigen. We also used the polymerase chain relation to detect hurnan papillomavirus DNA in inverted follicular keratosis from paraffin embedded tissue preparation. Results : 1. Seven of the 9 patients,vere male and the ages ranged fiom 36 to 77 years(mean 53 years). The lesions were situat d on the face(4/9),abdomen(1/9), back(1/9), chest(1/9), scapular area(1/9) and leg(1/9). The average size of the lesions was 1.5 cm. Verruca vulgaris was the most common clinical diagnosis(3/9), followed by seborrheic keratosis(2/9), soft fibroma(2/9), pigmented nevi(1/9), and granioloma pyogenicum(1/9). 2. Immunohistochemical stainiiigs using polyclonal antibodies to the human papillomavirus common antigen were negative for all 9 cases. 3. Polymerase chain reaction; using primers for human papillomavirus DNA were negative for all 9 cases. Conclusipn : In general, our linical findings are similar to those of others in previous studies. Our results of immunohistocheriiical staining and the polymerase chain reactions suggest, that in vert,ed follicular keratosis is ncl, related to the human papillomavirus. Further investigat.ions inf'o the nature of invert,ed follicular keratosis, should be centered on initated seborrheic keratosis and distinct follicular tumor s. (Korean J Dermatol 1997;35(6): 1074-1081)