Introduction. Primary cutaneous T-cell CD30+ lymphoproliferative disorders, such as lymphomatoid papulosis, primary cutaneous anaplastic large cell lymphoma and borderline types, may co-exist with other lymphomas, mainly mycosis fungoides. Furthermore, these diseases should be differentiated from large cell transformation of mycosis fungoides.

Objective. Special attention was focused on difficulties in differential diagnosis between primary and secondary proliferation with CD30+ expression.

Case report. We present a patient with mycosis fungoides in whom, in the course of the disease biopsy of the new skin lesions, revealed rich lymphoid infiltrates, consisting of above 80% large atypical cell, showing CD30+, CD4+ and CD3+ antigens expression. No internal organ involvement was observed. The patient was treated with good results according to CHOP regimen and PUVA method.

Conclusions. The presented case illustrates the diagnostic difficulties encountered in cases, in whom, mycosis fungoides coexists with CD 30+ lymphoproliferative disorders. Taking into account the prognosis and targed treatment, a proper diagnosis is of extreme importance.