Primary cutaneous large B-cell lymphoma, leg type, is a rare and aggressive neoplasm as defined by the World Health Organization/European Organisation for Research and Treatment of Cancer classification of cutaneous lymphomas. In some cases this disease may simulate other forms of benign or malignant solid tumours.We present a case of a 74-year-old man showing a quickly ‘migrant’ mass on his forehead. First skin biopsy, ultrasound and magnetic resonance images were not significant. A deeper biopsy revealed a pathology consistent with a primary cutaneous diffuse large B-cell lymphoma leg type.The patient was successfully treated with only local radiotherapy (total dose: 32.4 Gy). At 1-year follow-up there were no recurrences.To the best of our knowledge, this is the second case of a primary cutaneous diffuse large B-cell lymphoma leg type developed as a quickly ‘migrant’ lesion. In contrast with the first report, our case developed in a non-leg site. From these two cases, we should bear in mind that aggressive and quickly migrant cutaneous or subcutaneous masses might mask a lymphomatous disease.