The irritant response of perilesional skin is a serious limitation of dithranol therapy in psoriasis. No data are available on the actual prevalence and severity of irritation during 24-h dithranol treatment in an inpatient setting. Using a retrospective analysis of 68 patients with psoriasis visiting our inpatient department for dithranol treatment, the occurrence of dithranol irritation was studied. We found a relatively high frequency of dithranol irritation. Furthermore, most irritation occurs at the start of the therapy with relatively low concentrations.