The aim of this work was to study the effects of external dithranol therapy of psoriatic patients on the clinical status and serum calcitonin concentrations. This was done on 19 patients with common psoriasis using Cignoderm in the short contact therapy. Calcitonin concentration in serum samples was determined before and after a 14-day therapy. Results obtained before were compared with concentrations after dithranol treatment and with results in control group. Serum TSH was also measured in serum samples from both groups at the very beginning time. The determinations showed statistically significant lower serum TSH level in psoriatic patients before therapy vs. control and significant, negative correlation with calcitonin concentration in those patients. After a 14-day dithranol therapy a significant calcitonin concentration decrease as well as clinical effects were observed in the investigated group.