Background. Skin diseases (e.g., psoriasis and systemic sclerosis) are generally associated with negative psychosocial outcomes. Although different psychological interventions have been used to improve the quality of life of dermatological patients, the effects of the guided written disclosure (GWD) protocol have not been previously examined in these patients. Moreover, little attention has been paid to positive psychology constructs. Methods. This study investigates the effectiveness of GWD on positive and negative functioning in dermatological patients. Pre- and 1-month post-intervention measures included emotion regulation, sense of inner peace, skin-related symptoms and functioning, sense of coherence, and psychological distress. Results. A total of 196 consecutive outpatients were randomly assigned to GWD and active control groups, of whom 60 (30.6%) completed the study and 45 (GWD: n = 24; AC: n = 21) provided complete data. Our results did not show any significant difference between the experimental and control groups in the outcome variables, whereas non-completers reported higher levels of distress, unpleasant skin-related emotions, and lower cognitive reappraisal compared to completers. Conclusions. These findings show a poor compliance, and suggest that expressive writing is not well accepted by patients and is not effective in improving positive and negative psychological functioning in dermatological patients.