B 细胞幼淋巴细胞白血病 (B-PLL) 在世界卫生组织 (WHO) 第四版血淋巴肿瘤分类 (WHO-HAEM4) 中被认为是一个独特的实体；然而，其从头呈现已从即将发布的第五版分类（WHO-HAEM5）中删除。我们介绍了一名 65 岁男性的病例，其白细胞增多、疲劳，影像学显示无器官肿大。骨髓检查显示幼淋巴细胞群占骨髓成分的 78%。通过临床参数和辅助方法彻底排除其他实体后，我们得出结论，该病例代表 B-PLL 的新发病例。© 2024。日本血液学会。

B-cell prolymphocytic leukemia (B-PLL) was recognized as a distinct entity in the fourth edition of the World Health Organization (WHO) classification for hematolymphoid neoplasms (WHO-HAEM4); however, its de novo presentation has been removed from the upcoming 5th edition classification (WHO-HAEM5). We present a case of a 65-year-old man with leukocytosis, fatigue, and no organomegaly by imaging. Bone marrow examination showed a prolymphocytoid population comprising 78% of the marrow elements. After thorough exclusion of other entities by clinical parameters and ancillary methods, we concluded that this case represents a de novo case of B-PLL.© 2024. Japanese Society of Hematology.