We report a patient with phenytoin-induced pseudolymphoma mimicking cutaneous T-cell lymphoma (CTCL). Despite withdrawal of phenytoin, there was persistence of the cutaneous eruption and lymphadenopathy. Southern blot analysis of immunoglobulin and T-cell receptor genes was therefore used to assess whether there was a clonal lymphoid expansion. However, no rearrangement of the beta T-cell receptor gene or immunoglobulin heavy-chain gene was detected in tissue DNA from skin and lymph nodes. One year later the patient became asymptomatic, although he is still at risk of developing a true malignant lymphoma in the future, a condition known as pseudo-pseudolymphoma. It is suggested that genotypic studies may help in the initial diagnosis and the subsequent management of such patients.