We report the case of a 43-year-old man, suffering from ankylosing spondylitis and treated with Infliximab 5 mg/kg every 2 months, with an excellent disease control. During a follow-up consultation, an incipient renal insufficiency is detected. A urine analysis showed haematuria and proteinuria and a renal puncture-biopsy revealed an image of IgA nephropathy.Several cases of IgA nephropathy have been reported in the literature associated with ankylosing spondylitis. Some of them occur in patients treated with antitumour necrosis factor, but it is unclear whether this pathology is caused by the treatment or whether treatment failed to prevent its occurrence.Our clinical case highlights the importance of regular monitoring of renal function in patients with ankylosing spondylitis, as well as urinary spotting.The question of whether the disease itself, the treatment or other factors such as immune dysregulation could be held responsible for kidney disease will be addressed in the discussion.