Background: Classic hairy cell leukemia (HCL) typically presents with pancytopenia, monocytopenia, and splenomegaly; leukocytosis is uncommon and usually moderate. Cytogenetic abnormalities are infrequent, and trisomy 8 has rarely been reported. Case presentation: A 49-year-old man presented with progressive asthenia, pallor, epistaxis, gingival bleeding, and abdominal discomfort. Examination revealed massive splenomegaly. The complete blood count showed leukocytosis (41 × 109/L), anemia (hemoglobin 10.3 g/dL), and thrombocytopenia (43 × 109/L). The blood smear showed 77% small-to-medium-sized lymphoid cells with villous cytoplasmic projections, 19% lymphocytes, 4% neutrophils, and absolute monocytopenia (0%). Bone marrow aspiration was difficult (tendency to dry tap) and showed 83% infiltration by hairy cells. Flow cytometry identified a clonal B-cell population (CD19+, CD20+, FMC7+, CD10+, CD5−, CD23−, CD79b−, weak kappa) coexpressing CD25, CD103, and CD123. A heterozygous BRAF V600E mutation was detected. Karyotyping showed trisomy 8 in 20/20 metaphases. Conclusion: This case illustrates an uncommon hyperleukocytic presentation of classic HCL, with CD10 expression and trisomy 8, a combination that may mimic HCL variant or other splenic B-cell lymphomas. Integrated morphological, immunophenotypic, and molecular assessment, notably BRAF V600E testing, remains decisive for diagnosis and treatment choice.