A 63-year-old man with relapsed diffuse large B-cell lymphoma received autologous anti-CD19 chimeric antigen receptor (CAR) T-cell therapy after second-line treatment and bridging with rituximab, ifosfamide, carboplatin, and etoposide (R-ICE). He developed cytokine release syndrome (CRS) and immune effector cell (IEC)-associated neurotoxicity syndrome (ICANS), with an ICE score of 9/10, accompanied by peripheral facial paralysis and tetraparesis. Treatment with tocilizumab and dexamethasone was initiated. Magnetic resonance imaging showed no intracranial abnormalities. Cerebrospinal fluid (CSF) analysis revealed T lymphocytic pleocytosis, with CD3/CD19 CAR T cells present in the CSF. Cytocentrifuged and stained CSF preparations showed macrophages with hemophagocytosis of lymphocytes and erythrocytes, indicating macrophage activation syndrome/haemophagocytic lymphohistiocytosis (HLH). This toxicity resembling HLH (IEC-associated HLH-like syndrome) can manifest as a second inflammatory wave after initial improvement of CRS. The patient developed a second episode of ICANS and received methylprednisolone and dexamethasone. He was discharged on day 42 with improved general condition but limited mobility. Enrico Schalk performed the cytological and flow cytometric diagnostics, took the photomicrographs, and wrote the manuscript. The author declares no conflicts of interest and received no financial support. Data availability is not applicable. Figure 1 shows hemophagocytosis of lymphocytes and erythrocytes in CSF. Ethical approval and patient consent were not required. Permission to reproduce material from other sources is not applicable. Clinical trial registration is not needed. ORCID: 0000-0003-1892-5098. How to cite this article: Schalk E. Immune effector cell-associated haemophagocytic lymphohistiocytosis-like syndrome. eJHaem. 2024;5:881-82. https://doi.org/10.1002/jha2.950A 63-year-old man with relapsed diffuse large B-cell lymphoma received autologous anti-CD19 chimeric antigen receptor (CAR) T-cell therapy after second-line treatment and bridging with rituximab, ifosfamide, carboplatin, and etoposide (R-ICE). He developed cytokine release syndrome (CRS) and immune effector cell (IEC)-associated neurotoxicity syndrome (ICANS), with an ICE score of 9/10, accompanied by peripheral facial paralysis and tetraparesis. Treatment with tocilizumab and dexamethasone was initiated. Magnetic resonance imaging showed no intracranial abnormalities. Cerebrospinal fluid (CSF) analysis revealed T lymphocytic pleocytosis, with CD3/CD19 CAR T cells present in the CSF. Cytocentrifuged and stained CSF preparations showed macrophages with hemophagocytosis of lymphocytes and erythrocytes, indicating macrophage activation syndrome/haemophagocytic lymphohistiocytosis (HLH). This toxicity resembling HLH (IEC-associated HLH-like syndrome) can manifest as a second inflammatory wave after initial improvement of CRS. The patient developed a second episode of ICANS and received methylprednisolone and dexamethasone. He was discharged on day 42 with improved general condition but limited mobility. Enrico Schalk performed the cytological and flow cytometric diagnostics, took the photomicrographs, and wrote the manuscript. The author declares no conflicts of interest and received no financial support. Data availability is not applicable. Figure 1 shows hemophagocytosis of lymphocytes and erythrocytes in CSF. Ethical approval and patient consent were not required. Permission to reproduce material from other sources is not applicable. Clinical trial registration is not needed. ORCID: 0000-0003-1892-5098. How to cite this article: Schalk E. Immune effector cell-associated haemophagocytic lymphohistiocytosis-like syndrome. eJHaem. 2024;5:881-82. https://doi.org/10.1002/jha2.950