A 31-year-old man previously treated with chemotherapy for metastatic testicular cancer presented with new mediastinal lymphadenopathy and peripheral lung opacities. Serum tumour markers were not elevated and a PET (positron emission tomography) scan revealed increased FDG (fluoro-deoxyglucose) uptake in the lungs and mediastinum consistent with testis cancer relapse. A biopsy of a mediastinal lymph node was performed and the pathology was that of sarcoidosis. Immunohistochemistry however was positive for PLAP (placental alkaline phosphatase) and negative for EMA (epithelial membrane antigen). This immunohistochemical profile raised concerns that the observed pathology represented a sarcoid reaction to micro-metastatic testicular cancer relapse. We performed immunohistochemical pathology analysis on four known cases of sarcoidosis and found the same immunohistochemical-staining pattern. This case highlights the problem of specificity when interpreting the significance of PET scans and immunohistochemical analysis in this situation. Sarcoidosis, a condition that has been associated with testicular cancer, should always be considered in the differential diagnosis.