BACKGROUND The development of peripheral T-cell lymphoma (PTCL) after chemotherapy for Hodgkin’s lymphoma (HL) is rare, and highly aggressive TCL/leukemia has not been reported to date. The relationship between HL and PTCL needs further exploration to understand the pathogenesis of metachronous lymphoma (ML) and find effective treatment options. We report a patient with ML, whose biopsy of a right cervical lymph node initially confirmed classical HL (CHL). CASE SUMMARY We report a patient with ML, whose biopsy of a right cervical lymph node initially confirmed CHL, with typical reed–sternberg cells expressing CD30 and PAX-5. T-cell leukemia/lymphoma occurred 3 years after treatment, and a lymph node biopsy at the onset confirmed PTCL, nonspecific type, expressing CD3, CD4 and CD8. The patient was treated with standard doses of chemotherapy, programmed cell death-ligand 1 monoclonal antibody, and chidamide, all of which failed to achieve complete remission. The patient was diagnosed with refractory state, and eventually died of leukocyte stasis. CONCLUSION The accuracy of the diagnosis needs to be confirmed when chemotherapeutic drugs are not effective.