Background: MMP-9, a member of the gelatinase group of matrix metalloproteinases was found to play an important role in the development and progression of multiple solid cancers as well as Hodgkin lymphoma and lymphocytic leukemia.Objective: To detect the amount of expression and distribution pattern of MMP-9 in different cutaneous stages of mycosis fungoides (the commonest type of cutaneous TCL).Patients and Methods: The study included twenty two patients (with different cutaneous stages of mycosis fungoides) and 10 control subjects. Histopathological examination using routine staining with hematoxylin and eosin was done to confirm the diagnosis of mycosis fungoides. Immunohistochemical study of the amount and distribution pattern of MMP-9 using MMP-9 monoclonal anti – human antibodies was carried out.Results: A high expression of MMP-9 was found in MF cases, there was no dermal MMP-9 expression in controls and the difference was statistically significant (P. value < 0.001). A significant increase in the frequency and general intensity of expression of MMP-9 was detected as we progress from patch to plaque to tumor stages of MF (P. value = 0.000). MMP-9 staining in the epidermis changed significantly from basal cell pattern in 70% of the controls to a suprabasal single cell staining pattern in MF patients (P. value < 0.001), without significant change in the expression pattern of MMP-9 in the epidermis as we progress from patch to plaque to tumor (P. value = 0.124). The intensity of MMP-9 expression within dermal tumor cell aggregates was statistically higher in the tumor stage than in plaque stage than in the patch stage (P. value < 0.001). A significantly higher amount of blood vessels was found in MF sections when compared to controls (P. value < 0.001) While the intensity of MMP-9 expression in the endothelial cells within tumor cell aggregates did not change significantly upon progression from patch to plaque to tumor stages (P. value =0.169), it was significantly higher within tumor cell aggregates than outside the tumor cell aggregates (P. value= 0.015). Moreover, the intensity of MMP-9 in the endothelial cells outside the tumor cell aggregates did not differ from the controls (P. value = 0.118). No significant difference was found when comparing MMP-9 expression in different clinical stages of MF (P.value= 0.218).Conclusion: MMP-9 plays an important role in MF through facilitation of epidermotropism and helping in the local progression of the lesions from patch to plaque to tumor as it allows the invasion and spread of malignant T cells. Moreover, it is produced by the endothelial cells and plays a role in angiogenesis which was found to be increased in MF cases. Targeting MMP-9 could provide a therapeutic mean of controlling progression and spread of MF