ABSTRACTThis present study is a sub-project of the Danish research project Bullying and Harassment at work: Prevalence, Risk factors, Consequences, Prevention, and Rehabilitation 2006-2009 which is a prospective research project initiated by the Danish National Research Centre for the Working Environment. The data material originates from a comprehensive base-line and follow-up questionnaire administered in 2006 and in 2008. The purpose of this quantitative study was to assess the extent to which bullying at work would affect those who were not experiencing the direct impact of the bullying behaviour, but who reported to witness the bullying of others in their work unit. Both a cross-sectional and a longitudinal methodological approach were employed in order to investigate both the short- and long-term effects of witnessing bullying at work. In line with results obtained in previous cross-sectional studies, it was expected that the non-bullied witnesses to workplace bullying would experience elevated levels of stress, burnout, psychosomatic symptoms, and state negative affect, and lower levels of general health than a control group. Due to the prospective design of the Workplace Investigation, it was also possible to assess the potential long-term effects of being a witness to bullying at work by comparing those who reported to witness bullying at both T1 and T2 (i.e long-term witnesses) to a control group, previous witnesses, and new witnesses at T2. The results from the cross-sectional approach revealed that the self-declared witnesses to bullying in 2006 and in 2008 were significantly more affected with regards to all the respective measures than the control group in 2006 and in 2008. The longitudinal analysis, however, yielded both supportive and contradictive results in terms of the stated hypotheses.