SummaryFactor XLLLa‐positive dermal dendrocytes (FXIIIa+dd) may have an important role in the pathogenesis of psoriasis, in that their numhers are increased in lesional skin compared with non‐lesionai skin. Moreover, in AIDS‐associated Kaposi's sarcoma the number of these cells is also increased, in comparison with the classical type of Kaposi's sarcoma. In addition, patients suffering from HIV‐1 infection may develop severe psoriasis.The aim of this study was to examine the distribution of FXIIIa+dd in lesional and non‐lesional skin from seven psoriatic patients with positive HIV‐1 serology. and compare the results with age‐, sex‐, and site‐matched HIV‐1‐negative psoriatic patients. In both patient groups there was an increase of FXIIIa+dd in the papillary dermis in lesional skin, compared with non‐lesional skin (HIV+[P=0.0007]: HIV−[P=0.0006]). Positive cells were also observed within the epidermis in lesional skin in both groups. However, there was no significant difference between HIV‐1+and HIV‐1−groups in the number of FXIIIa+dd in the epidermis and dermis (P>0.05). These findings suggest that, if FXIIIa+dd do have a role in psoriasis, deterioration of this condition in HIV‐1+patients is not due to pr