Nucleophosmin 1 (NPM1) is an abundant phosphoprotein mainly located in the nucleolus but also shuttling between the nucleus and cytoplasm. NPM1 has been proposed to be involved in synthesis and processing of ribosomal RNA, regulation of chromatin structure and transport of rRNA and ribosomal proteins. NPM1 gene is considered to be implicated in human cancer as it is a frequent target of genetic alterations, primarily in haematopoietic neoplasms. We describe a case of a therapy-responder acute myeloid leukaemia (AML) patient bearing two novel NPM1 mutations. Cells' transfection studies indicate that the presence of one of these mutations is associated to an abnormal nucleolar structure, suggesting that NPM1 may contribute to the control of nucleolar integrity.