[Primary septic arthritis is a rare, atypical manifestation of invasive meningococcal disease].

: We present a case report of a 50-year-old man diagnosed with a primary septic arthritis with invasive Neisseria meningitidis serogroup W (MenW) clonal complex 11 identified with culture in blood and synovial fluid. The patient recovered from rapidly instituted relevant antibiotics and synovectomy, but there may be a risk of fatal delayed diagnosis and treatment by an atypical manifestation of invasive meningococcal disease. Invasive MenW disease has been increasing in recent years and has been described with atypical presentations.