SummaryA residual mass after treatment of Hodgkin’s disease points to the diagnosis of fibrotic residue or of persistent disease. Radiological and radionuclide imaging, although helpful, cannot differentiate between both conditions with absolute certainty. Thus, residual masses are followed up: stable or regressive masses strengthen the hypothesis of fibrotic residue, while enlarging masses evoke relapsing disease. We report on a patient with an enlarging residual mass after completion of therapy, which proved to be a benign thymic hyperplasia after histological analysis. Previously reported similar observations are reviewed.