Therefore, we set out (i) to investigate the expression of mGluR5 in patients with classical Hodgkin lymphoma (some with and some without a prior encephalitis), (ii) to investigate mGluR5 positivity on CD30+ Hodgkin and Reed–Sternberg cells from biopsy material of these patients, and (iii) to analyze the transcriptome of various established classical Hodgkin lymphoma cell lines for a correlation between mGluR5 mRNA expression and downstream target activation that might promote tumor growth. Here, GRM5 is linked to encephalitis.