Amyloidosis is a heterogeneous group of diseases characterized by the extracellular deposition of amyloid proteins in various tissues and organs, which leads to significant morbidity and mortality. The most commonly affected organs include the kidneys, liver, spleen, heart, and nervous system, where the deposition of amyloid proteins disrupts normal function and causes a wide range of clinical manifestations. Involvement of osseous structures, particularly the ribs, is exceedingly rare and has not been extensively documented in the medical literature, making it a subject of significant clinical interest. This study aims to present a rare and fortuitously discovered case of costal amyloidosis in a patient who initially presented with a chest wall mass. The patient’s presentation, diagnostic workup, and subsequent management are detailed to provide a comprehensive overview of this unusual manifestation of amyloidosis. Clinical evaluation revealed a firm, non-tender mass on the chest wall, prompting further investigation. Biological analyses included a series of laboratory tests to rule out common differential diagnoses and identify potential systemic involvement. Radiological evaluation comprised of advanced imaging techniques, including chest X-ray, computed tomography (CT), and magnetic resonance imaging (MRI), which highlighted the nature and extent of the osseous involvement. A biopsy of the mass was performed, and histopathological examination confirmed the diagnosis of amyloidosis through the identification of amyloid deposits using specific staining techniques. The case also examines the evolutionary aspects of the disease, discussing the progression and changes observed over time through regular follow-ups. Therapeutic strategies were implemented based on the latest guidelines and tailored to the patient's specific condition, including both pharmacological and surgical interventions. The short-term and long-term outcomes of these interventions are analyzed, highlighting the challenges and successes encountered during the treatment process. By presenting this case, we aim to shed light on the rare occurrence of costal amyloidosis, its diagnostic challenges, and therapeutic considerations. This case underscores the importance of considering amyloidosis in the differential diagnosis of chest wall masses and contributes to the broader understanding of the disease's clinical spectrum. Additionally, it emphasizes the necessity of a multidisciplinary approach in managing such rare and complex cases, ensuring comprehensive care and improved patient outcomes.