Folliculotropic mycosis fungoides is associated with a worse prognosis than classical mycosis fungoides (MF), but whether this is due to resistance to skin-directed therapy or to biological differences is unclear. We discuss a case of a patient with folliculotropic MF (stage IIA) who progressed to develop Sézary syndrome (SS), stage IVB, over 6 years. A 40-year-old man presented with pruritic plaques affecting his head and trunk, characterized by follicular plugging. The histology was consistent with folliculotropic MF and T-cell gene analysis studies revealed a T-cell clone in the skin only. His condition gradually deteriorated and 5 years after presentation, T-cell gene analysis studies revealed the presence of a clone in the blood identical with that seen in the skin. His condition progressed with the development of erythrodermic disease and a leukaemic blood picture and he subsequently died of systemic nodal and visceral involvement. We present the first report detailing the stepwise progression of a patient with stage IIA folliculotropic MF to SS. This case demonstrates that MF and SS represent a clinical spectrum of the same disease.