A case of CD5-positive diffuse large cell lymphoma in a patient with autoimmune hemolytic anemia (AIHA) is reported. The patient was diagnosed with AIHA in December 1988. Three and a half years later, the patient complained of fever and left sided flank pain. Abnormal lymphocytes appeared in the peripheral blood and were positive for HLA-DR, CD5, CD19, CD20, and surface immunoglobulin (mu, lambda). The pathological diagnosis of the cervical lymphnode was non-Hodgkin lymphoma; diffuse large cell type with a starry sky-like appearance. Although the 8q24 translocation was not detected by karyotypic analysis of the peripheral blood mononuclear cells (PBMNC), Southern blot analysis revealed that the c-myc rearrangements had occurred. This case showed two rearranged bands with Eco RI, Bam HI, or Bgl II digestion, and a germline band with Hin dIII digestion using a second exon fragment of the c-myc gene as a probe. Despite intensive chemotherapy, this patient died 6 months after being diagnosed with malignant lymphoma. We discuss the c-myc rearrangements in this aggressive CD5-positive diffuse large B cell lymphoma.