The marked photosensitivity associated with chronic actinic dermatitis (CAD) is presumed to be due to a T cell-mediated response to ultraviolet (UV)-induced epidermal neoantigens. Photosensitivity is, however, a rare occurrence in cutaneous T-cell lymphoma (CTCL). We discuss a series of four patients with erythrodermic CTCL who exhibited marked photosensitivity mimicking CAD. Significantly, the tumour cells had a CD8 phenotype in half of these patients. All patients had T-cell clones in skin and also demonstrated identical peripheral T-cell clones in blood or lymph node involvement. Sézary cell counts ranged from 6% to 20%, CD4/CD8 ratios from 0.22 to 23.5. Clinical presentation was striking for a marked photosensitive distribution. Monochromator irradiation testing revealed reduced minimal erythema doses throughout UVB and UVA ranges, findings consistent with those seen in CAD. All patients subsequently died from systemic disease. These findings suggest that, rarely, malignant clonal T-cell populations may recognize a unique UV-induced neoantigen, resulting in the clinical features of severe photosensitivity mimicking those seen in CAD.