We present a case of cutaneous lymphoma with photosensitivity. We consider “cutaneous lymphoma” as a primary malignant lymphoma of the skin, and not as mycosis fungoides. We made an initial diagnosis of actinic reticuloid. However, there were some clinical aspects and laboratory findings which were not compatible with the criteria for actinic reticuloid in our case: the age of the patient at onset of the skin eruption was too young, and no severe photosensitivity was found within a wide range of ultraviolet radiation. In addition, immunohistochemical examination indicated marked proliferation of CD4 + T cells in the skin. Monoclonal rearrangement of the T cell receptor gene around the infiltrating cell was recognized with Southern blotting technique. From these findings, we selected “cutaneous lymphoma with photosensitivity” as the most suitable diagnosis.