Horizontal violence among nurses is recognized as a major problem in hospitals; however, the origins and effects on patient care have not been studied. This study described the incidence of horizontal violence among hospital staff RNs and tested 2 hypotheses about the social origins of this behavior. A random sample of 175 hospital staff RNs drawn from the California Board of Registered Nursing's mailing list was surveyed. Horizontal violence was reported by 21.1% (n = 37) of participating nurses. Hypotheses were supported. Findings suggested (a) a positive relationship between beliefs consistent with an oppressed self and horizontal violence (r = .434, P < .05) and (b) a positive relationship between beliefs consistent with those of an oppressed group and horizontal violence (r = .453, P < .05). A change in the oppressive social structure of hospitals may be needed to truly address horizontal violence in the best interest of the quality and safety of patient care.