Background: Unilesional mycosis fungoides (MF) is a rare variant of cutaneous T-cell lymphoma (CTCL), characterized by a solitary lesion clinically and by histopathological features indistinguishable from those of MF, and typically having a benign course. Objective: To describe the clinicopathological features of a series of patients with unilesional MF. Methods: The records of cases of unilesional MF identified during a 10-year period in two medical departments were reviewed. Results: There were 7 patients: 6 males, 1 female; mean age at the time of diagnosis: 32 years; age range: 12–58 years; 3 were below the age of 18 years. The mean pretherapy follow-up period was 9 years (range: 2–20 years). In 5 patients, the eruption consisted of a characteristic patch or plaque of MF located on the trunk or upper extremity; in 2 it was atypical – in 1, a hypopigmented patch, and in 1, a plaque indistinguishable from MF-associated follicular mucinosis. Histopathologically all the lesions exhibited features characteristic of MF, with CD3+ lymphoid cells. In 6 cases (with available fresh frozen tissue) there was a predominance of CD3+ CD4+ cells; in 1 of 5 there was deletion of CD7, and in 3 of 5 there was an overexpression of IL-2 receptor. T-cell receptor γ gene rearrangement was found in 1 of 4 cutaneous lesions tested; in 2 cases it was found in the blood but not in the skin. Treatment modalities included localized electron beam, excision, topical nitrogen mustard or topical steroids and sunbathing, resulting in all cases in a sustained complete clinical response. In 1 patient, however, there were 2 local recurrences and in yet another patient there was distant cutaneous spread 3.5 years after therapy. Conclusions: Unilesional MF is a rare variant of CTCL, has heterogeneous clinical manifestations and can affect any age group, including children. The histopathological and immunophenotypical features are in general indistinguishable from those observed in multilesional MF. Although it is a unifocal event, there may occasionally be cutaneous spread with the appearance of noncontiguous lesions, even a long time after therapy. Whether all cases represent minimal-stage IA MF or whether some are actually T-cell pseudolymphoma remains to be clarified.

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