We identified a consanguineous Moroccan family with three affected siblings diagnosed with rheumatoid factor-negative polyarticular juvenile idiopathic arthritis. They all suffered from an early-onset (2-4 years-old) chronic and symmetric polyarthritis affecting both large and small joints. The joint involvement was markedly erosive in two siblings, with the older sister requiring hip prosthetic replacement at the age of 18 years. None of the patients had fever, skin rash, uveitis or other extra-articular manifestations. Laboratory analyses revealed leukocytosis, thrombocytosis, severe anaemia, marked increase of inflammatory markers and negative results for rheumatoid factor, anti-nuclear antibodies and HLA-B27