Evidence-based psoriasis treatment guidelines may help physicians overcome uncertainties in initiating and monitoring systemic treatment and have thus been suggested as a tool for improving the care provided to psoriasis patients. A prospective cohort study of dermatologists' prescription behaviour was performed with two consecutive documentation periods (before and after the publication of the guidelines). 49 dermatologists were asked to provide continuous documentation of their treatment choices for patients with psoriasis by filling in a standardised documentation form. In addition, a questionnaire consisting of eight items was used to assess familiarity with, attitudes towards, and the impact of the psoriasis guidelines on the participating dermatologists. 49 dermatologists documented their treatment choices during 4,491 patient visits before and 4,120 visits after the publication of the German national psoriasis treatment guidelines. The average proportion of prescribed systemic treatments for patients with moderate to severe psoriasis increased from 31 to 35% after the guidelines were published. 80% of the participants stated that the guidelines had led to changes in their treatment decisions, whereas only 20% stated that the guidelines had had no impact in this regard. All but one participant considered the guidelines "useful" or "very useful". The results of the study show that guidelines can be an important tool for improving the quality of care provided to patients with psoriasis.