Background: During therapy of patients with mycosis fungoides (MF) at the Department of Dermatology, Kasr El-Aini Hospital, follow-up biopsies are routinely taken every 2 months. It was noticed that lesions of MF might become clinically normal during treatment, and yet still showmicroscopical evidence of MF. This finding raised the possibility that clinically normal skin in MF could be microscopically involved. Aim: The aim of our work was to evaluate the degree of histopathological involvement of normal-looking skin in patients with MF. Patients and methods: Thirty patients with stage IB were biopsied from their normal skin. Two biopsies were taken: one proximal (2 cm) and the other distal (> 5 cm) from any visible lesion. Ten normal controls were included in the study. All specimens were stained with H&E and examined microscopically. The microscopical diagnosis was confirmed by immunophenotyping. Results: Epidermotropismwas detected in 21 (70%) of the proximal skin biopsies and 14 (47%) of the distal skin biopsies, whereas no biopsy from the control group showed epidermotropism. All the proximal skin biopsies showed dermal infiltrate and 90%of the biopsies from the distal normal skin showed dermal infiltrate (mostly superficial perivascular). Conclusion: Normal skin in patients with MF could be affected microscopically and this may raise questions regarding the credibility of the current staging classification of MF, and may necessitate taking biopsies from normal skin before starting topical treatment. During MF treatment, biopsies from cured lesions are required before starting withdrawal. Background: During therapy of patients with mycosis fungoides (MF) at the Department of Dermatology, Kasr El-Aini Hospital, follow-up biopsies are routinely taken every 2 months. It was noticed that lesions of MF might become clinically normal during treatment, and yet still showmicroscopical evidence of MF. This finding raised the possibility that clinically normal skin in MF could be microscopically involved. Aim: The aim of our work was to evaluate the degree of histopathological involvement of normal-looking skin in patients with MF. Patients and Methods: Thirty patients with stage IB were biopsied from their normal skin. Two biopsies were taken: one proximal (2 cm) and the other distal (> 5 cm) from any visible lesion. Ten normal controls were included in the study. The microscopical diagnosis was confirmed by immunophenotyping. Results: Epidermotropism was detected in 21 (70%) of the proximal skin biopsies and 14 (4 7%) of the distal skin biopsies, as no biopsy from the control group showed epidermotropism. All the proximal skin biopsies showed dermal infiltrate and 90% of the biopsies from the distal normal skin showed dermal infiltrate (mostly superficial perivascular). Conclusion: Normal skin in patients with MF could be affected microscopically and this may raise questions regarding the credibility of the current staging classification of MF, and may necessitate taking biopsies from normal skin before starting topical treatment. withdrawal.