Disseminated superficial actinic porokeratosis (DSAP) is a rare keratinization disorder with potential malignant transformation, for which present treatment strategies show limited success. In a retrospective study the response of DSAP lesions to grenz ray radiotherapy (RTx) was evaluated. Data of patients treated with RTx at University Hospital Zurich, Switzerland, between 2004 and 2015, were reviewed. Patients with DSAP, who received at least 1 RTx treatment session and who had been followed up for at least 4 weeks were included in the further data analysis. The study cohort consisted of 8 patients with a median age of 73 years. All were treated with grenz rays for DSAP. 7 of 8 patients showed complete clinical clearing of the lesions.