Diagnosis of cutaneous T-cell lymphomas, especially of mycosis fungoides is often difficult in the early stage of the disease, as well as their differentiation from other reactive inflammatory dermatoses. The diagnostic exactness could be improved by the simultaneous histological, immunophenotypic and gene rearrangement analysis of the skin biopsy specimen, and these results together with the clinical findings could help to establish the early diagnosis. Using this complex analysis effective treatment can be started in time and repeated skin biopsies are not always necessary. Authors performed this complex investigation in skin biopsy specimens and peripheral blood of 49 patients with cutaneous T-cell lymphoma and other T-cell lymphoproliferative diseases and estimated the diagnostic value of the T-cell receptor gamma gene rearrangement analysis. Based on the results of the clinical, histological, immunophenotypic and gene rearrangement studies authors could made a clear distinction between the benign dermatoses (19 cases) and malignant cutaneous lymphomas (17 cases). However less than one third of the patients (13 cases) remained unclassified, so definite diagnosis of these cases could be based on the long term follow up and on the results of the repeated skin biopsies.