AA amyloidosis might be a serious complication of chronic inflamatory diseases. One of the possible causes of AA amyloidosis is ankylosing spondylitis (AS). Amyloidosis is a rare complication of AS. However, delayed diagnosis and therefore delayed treatment of the underlying disease may even lead to organ dysfunction. Organ dysfunction is a result of extracellular deposits of the acute-phase reactant - serum amyloid A (SAA). Renal involvement is the most common with clinical presentation characterised by proteinuria, nephrotic syndrome and chronic kidney disease. We present a case of a 45-year-old man with a 25-year history of untreated AS which has led to AA amyloidosis and a necessity of a renal replacement therapy. On admission patient denied arthralgia. Following further investigation AS was diagnosed as the underlying cause of amyloidosis manifesting as a nephrotic syndrome.