Anti-C1q autoantibodies have been proposed as a useful marker in SLE. This study aimed at measuring serum levels of anti-C1q antibodies in patients with SLE and investigates correlations of this level with the histopathological classes of renal biopsies and disease activity. The anti-C1q antibody level was measured in 30 females SLE patients and 20 controls. The activity of SLE disease was calculated according to the SLE disease activity index. A renal biopsy from patients with clinical manifestations of renal disease was obtained. There was a significant increase in the level of anti-C1q antibodies in SLE patients than controls and in patients with active LN than inactive LN (P