SLE is characterized by overproduction of various types of autoantibodies. Under certain circumstances, antibodies targeting some of the neoepitopes of the complement system can be seen. The most studied among antibodies directed against a component of the complement system is anti-C1q. Anti-C1q antibodies are present in approximately one third of the patients with lupus, who often have high clinical disease activity and in particular renal involvement. In the presence of high titers of anti-C1q antibodies also the levels of C1q and C3 and C4 components of the complement system are also usually low. The presence of the anti-C1q antibodies is not limited or specific just for SLE or lupus nephritis. For the first time, they were described in HUVS (Hypocomplementemic Urticarial Vasculitis Sydrome), later in Felty's syndrome, rheumatoid vasculitis, hepatitis C, poststreptococcal glomerulonephritis or aging population.