The complement system is a major component of innate immunity. Under normal conditions the contribution of the complement system is beneficial, but when inappropriately activated it may cause damage to the host and under certain conditions it may even be the target of an autoantibody response. Autoantibodies directed against individual complement components, convertases, complement regulators and complement receptors have been described. The presence of autoantibodies in individuals may be associated with manifestations of disease, but only for some autoantibodies have clear causal relations been described. Autoantibodies against complement components can even be present in healthy individuals, indicating that the development of pathology most likely requires the simultaneous action of multiple processes. Since autoantibodies against complement components may cause depletion of circulating complement levels, leading to a secondary complement deficiency, it is imaginable that this process leads to an increased susceptibility to infections. In the present review, we describe autoantibodies against complement components and their subsequent effects.