This is a case report of recurrent meningococcal infection in a young woman. She had no positive microbiological findings but was serologically diagnosed with the meningococcal antibody test. Investigation of
the complement system showed no function of the terminal pathway. Further genetical analysis revealed a
pathogen mutation in the C8B gene in the patient and her sister. They were both immunised with meningococcal vaccines. Complement deficiencies are rare but potentially fatal. Workup for complement deficiency is
important for correct acute and prophylactic treatment.