Objective To find out the pathologic changes and possible influencing factors in the process of spontaneous regression of plane warts.Methods One hundred and five lesional specimens taken from patients with plane warts were observed microscopically.Results The histologic features indicated slight hyperkeratosis,acanthosis and ballooning degeneration of keratinocytes in stable lesions;a combination of tower-peak shaped hyperkeratosis,cuneate hypergranulosis and ballooning degeneration in progressively increasing lesions;and infiltration of lymphocytes and necrosis of keratinocytes in inflammatory icthing lesions.Conclusions Specific cell-mediated immunity against keratimocytes may be involved in the process of regression of plane warts.There is a positive correlation between the activity of skin lesions and the induction of cellular immunity.