C1q deficiency in both humans and mice is strongly associated with autoimmunity. We have previously shown that bone marrow transplantation (BMT) restored C1q levels in C1q-deficient (C1qa(-/-)) mice. Here, we studied the effect of BMT on autoimmunity in C1qa(-/-) mice. Following irradiation, young C1qa(-/-) or wild-type MRL/Mp mice received bone marrow cells (BMC) from strain-matched wild-type or C1qa(-/-) animals. C1q levels increased rapidly when C1qa(-/-) mice received BMC from wild-type mice. Conversely, they decreased slowly in wild-type mice transplanted with C1qa(-/-) BMC. C1qa(-/-) animals transplanted with C1qa(-/-) BMC demonstrated accelerated disease when compared with wild-type mice given wild-type BMC. In contrast, a significant delay in the development of autoantibodies and glomerulonephritis was observed in C1qa(-/-) mice reconstituted with wild-type BMC, and the impaired clearance of apoptotic cells, previously described in C1qa(-/-) mice, was rectified. Moreover, the autoimmune disease was accelerated in wild-type mice given C1qa(-/-) BMC compared to animals transplanted with wild-type cells. These results provide supporting evidence that BMT may be a therapeutic option in the treatment of autoimmunity associated with human C1q deficiency.