Self-serving attributional bias is the tendency for a subordinate to attribute personal (internal) cause for successful performance but to assign cause for failures to external factors. The actor-observed difference in attribution is the tendency for concerned observers (managers) of a subordinate's performance to attribute cause for the performance to factors internal to the subordinate, in direct opposition to the subordinate's external attribution for the same performance. This research investigated both phenomena. Twenty-four experienced managers served as manager/subjects in simulated appraisal situations. Subjects with prior work experience served as subordinate/subjects. Each manager participated in four separate simulated performance appraisals, under differing conditions of objective performance and work history, for a total of 96 interactions. The results revealed a strong self-serving bias on the part of subordinates. The results also strongly supported the notion of an actor-observer difference in performance attribution. Subordinates tended to attribute more externally and managers tended to attribute more internally (to the subordinate), regardless of performance level. The research also served to delineate and articulate the relationship between self-serving bias and actor-observer differences.