Patient participation in treatment decisions can have positive effects on patient satisfaction, compliance and health outcomes. The objectives of this study were to examine attitudes of psoriasis patients regarding participation in treatment decisions and to evaluate the effect of a decision-aid for discussing treatment options. A "quasi experiment" was conducted in a large dermatological hospital in Italy: a questionnaire evaluating the decision-making process and treatment knowledge was self-completed by 231 consecutive psoriasis patients after routine clinical practice and by a second sample of 171 patients exposed to a decision-board. In routine clinical practice 67.9% of patients wanted to be involved in decision-making, 28.4% wanted to leave decisions entirely to the doctor and 3.7% preferred making decisions alone. 17.9% and 25.3% of the control and decision-board group had good knowledge. At multivariate analysis good knowledge increased the likelihood of preferring an active role (risk ratio (RR) = 2.21; 95% confidence interval (CI) 1.3-3.9; p = 0.006). The decision-board only marginally improved patient knowledge and doctor-patient communication. In conclusion, large proportions of psoriasis patients want to participate in decision-making, but insufficient patient knowledge can represent a barrier.