Indeterminate cell histiocytosis is a rare disease belonging to the group of malignant histiocytic diseases. The disease predominantly affects the skin. The disease appeared in the described patient at the age of 80 years. Morphs began to develop on the skin and rapidly spread over the whole body including the face. Only the hands and feet were left uncovered. The patients skin samples were taken from 2 sites for histological examination. The resulting conclusion was indeterminate cell histiocytosis. The treatment we chose was analogous to the procedures for Langerhans cell histiocytosis. We chose PUVA phototherapy as the first-line treatment. This treatment is frequently efficient for skin forms of Langerhans cell histiocytosis. In the described case, however, PUVA phototherapy did not influence the disease activity at all. As the second-line treatment, we used low-energy electron beam irradiation in the total dose of 36.2 Gy. This treatment had a positive impact, morphs began to diminish and slowly disappear from the skin. But they have not disappeared completely, therefore we assessed the treatment effect of the radiotherapy itself as partial remission of the disease. Within the third-line treatment, we used 2-chlorodeoxyadenosine in a dose of 5 mg/m2/per day, administered via subcutaneous injection over 5 consecutive days in monthly intervals. There were three cycles of this treatment administered overall. The treatment with 2-chlorodeoxyadenosine was tolerated without any adverse effects. The patient aged 82 years was only administered 3 cycles of 2-chlorodeoxyadenosine. When after the 3rd cycle the skin was free from any pathological morphs and only some pigmentation spots remained, we finished the treatment. The skin expressions of indeterminate cell histiocytosis completely disappeared after electron beam irradiation and the following administration of 3 cycles of 2-chlorodeoxyadenosine. The remission was short, however, after 6 months the disease recurred and the treatment is planned to resume. We assume the disease regresses following administration of 2-chlorodeoxyadenosine, but more than 3 treatment cycles will probably be needed to reach a longer-term response.Key words: electron beam irradiation - indeterminate cell histiocytosis - 2-chlorodeoxyadenosine.