The present disclosure relates to stable aqueous solutions comprising a high concentration of an anti-C5 antibody (e.g., ravulizumab) and methods for preparing the solutions. The disclosure also provides methods for treating or preventing complement-associated disorders, such as paroxysmal nocturnal hemoglobinuria (PNH) and atypical hemolytic uremic syndrome (aHUS), using the solutions. Also featured were therapeutic kits containing one or more of the solutions and a means for administering the solutions to a patient in need such a treatment.