In AL amyloidosis, amyloid fibrils, composed of abnormal light chain proteins, are produced by abnormal plasma cells in the bone marrow. AL amyloidosis is a plasma cell disorder but as the plasma cells are not truly cancerous, it is not regarded as a cancer. It is however closely related to myeloma and is diagnosed in 10–20% of myeloma patients. This guide discusses the clinical features of AL amyloidosis, its diagnosis and monitoring, and treatment and monitoring.