<p>Nucleolar stress has emerged as a critical regulatory mechanism linking ribosome biogenesis defects to apoptotic cell death in various pathological conditions. Fibrillarin (FBL), the catalytic component of box C/D small nucleolar ribonucleoproteins, participates in multiple forms of programmed cell death through both p53-dependent and p53-independent pathways across diverse disease contexts including cancer and neurodegeneration. In malignancies including breast cancer, colorectal cancer, and hepatocellular carcinoma, FBL overexpression promotes apoptosis resistance, whereas in Alzheimer’s disease and ALS/FTD, FBL dysfunction contributes to pathological neuronal death. Dysregulation of FBL can lead to excessive apoptosis or apoptosis resistance depending on cellular context and disease state. Various cellular stressors trigger aberrant FBL function, disrupting rRNA processing and ribosome assembly, which then activates nucleolar stress responses that culminate in cell death through ribosomal protein-MDM2-p53 axis activation or selective translational control of survival factors in a context-dependent manner. Therefore, targeting FBL-mediated apoptotic pathways is considered an important avenue for the treatment of various cancers and neurodegenerative diseases. In this review, we summarize the major and recent findings focusing on the mechanisms of FBL-regulated apoptosis in disease pathogenesis and provide a systematic overview of current therapeutic strategies targeting nucleolar stress pathways, including RNA polymerase I inhibitors and precision medicine approaches based on p53 status, which may provide important therapeutic targets that merit further investigation.</p>