A 30-year-old woman was referred for a positron emission tomography/computed tomography (PET/CT) scan with [F]fluorodeoxyglucose ([F]FDG) for staging of Hodgkin lymphoma (HL), nodular sclerosis type, diagnosed by biopsy of a bulky mediastinal mass. The scan demonstrated tracer uptake in the cervical lymph nodes bilaterally, in the bulky mediastinal mass and in the lungs, spleen and some lumbar and sacral vertebral bodies (top left). A PET/CT scan performed 1 month after completion of treatment (doxorubicin, bleomycin, vinblastine, dacarbazine, six cycles) showed complete metabolic response (centre of top left image). This finding was confirmed by another PET/CT performed 3 months later. Seven months after the end of chemotherapy, a follow-up PET/CT showed an intense tracer uptake [standardized uptake value (SUV)max = 4AE1 g/ml] in the left supraclavicular region (black arrow, right of top left image), suspicious for lymph node recurrence of HL. A contrast enhanced CT performed 3 d after the PET/CT showed a 20 · 14 mm oval nodule located medially to the jugular vein, suspicious for malignant adenopathy (lower left). A fused PET/ CT axial image showed increased [F]FDG uptake in the solid component of the nodule (right of lower left image). The lesion was resected. Histopathological examination (right) showed well-represented thymic compartments, including cortical (white arrow) and medullary areas (white arrowhead). In addition, a well-formed Hassal’s corpuscle was recognizable (black arrow) (Haematoxylin and Eosin, 200·). Thymic hyperplasia after chemotherapy is a common phenomenon in children and can occasionally be observed in young adults. This phenomenon has seldom been described in older adults. A normal variant in which the thymus extends superiorly to the left brachiocephalic vein and anteriorly to the brachiocephalic artery or left common carotid artery can occur. This can be visualized on CT as a soft tissue nodule that can mimic superior mediastinal adenopathy. In paediatric patients, [F]FDG uptake in a superior mediastinal nodule can be correctly attributed to ectopic thymus whether the intensity of [F]FDG SUVmax or the morphological characteristics are similar to the thymus. In the present case, the lack of significant thymic activity, the absence of thymic enlargement in the anterior mediastinum, the cervical involvement at first diagnosis, and the CT appearance of the soft tissue nodule led to the erroneous suspicion of recurrence of lymphoma. This report shows that increased [F]FDG uptake in hyperplastic ectopic thymic tissue following chemotherapy can also occur in adult patients. This rare normal variant should be kept in mind in PET/CT studies in patients with HL.