Background : Telomeres shorten with successive cell divisions in normal somatic cells. Telomeres cap chromosome ends and protects them from degredation. The maintenance of telomeres requires telomerase activity which is a ribonucleoprotein enzyme that catalyzes the addition of telomeric repeats to telomeres. Telomerase activity was decteted in malignant skin disorders and in inflammatory dermatoses. Aim of the work : The aim of this study is to determin quantitively the difference in the level of telomerase activity in psoriasis (one of the inflammatory dermatoses) and mycosis fungoides (one of the malignant skin conditions) to clarify the role of telomerase in both diseases.Methods : This study includes 15 psoriatic patients, 15 mycosis fungoides and 15 control cases. Two punch biopsies were taken from fresh sunprotected lesions of each case psoriasis and mycosis fungoides. One biopsy for histopathological confirmation of the diagnosis while the other was stored -80°c till PCR Elisa assessment of telomerase activity.Results : Results of the present study showed that there is no telomerase activity in normal skin. In psoriasis telomerase activity was positive in 80% of patients, and telomerase activity was correlated to disease duration. In mycosis fungoides telomerase activity was positive in 60% of patients and was correlated to the stage of mycosis fungoides, the more advanced disease stage the higher the telomerase activity. Conclusion : The results of this study indicate high telomerase activity in psoriatic and mycosis fungoides patients, suggesting that telomerase might play an important role as a biomarker for the prognosis and diagnosis of both diseases.