Pityriasis lichenoides in children: a long-term follow-up of eighty-nine cases. Pityriasis lichenoides is usually classified into an acute and a chronic form. From a review of 89 cases of the disease seen since 1974 it seems that a more realistic classification into three main groups, according to the distribution of pityriasis lichenoides lesions, could be made, namely, a diffuse, a central, and a peripheral form, each characterized by a different clinical course. Conversely, no correlations were detected in our series between the severity of skin lesions and their distribution or the overall course of the disease. None of our cases suggests the possible evolution of pityriasis lichenoides into lymphomatoid papulosis. Although no infectious causative agent has been identified, a viral origin seems likely in some cases. Most patients responded favorably to UVB irradiation. Our conclusions are (1) that pityriasis lichenoides is probably a clinical disorder with a diverse etiology and (2) that its classification by distribution seems more useful than its subdivision into an acute and a chronic form. 