This study is a replication and extension of previous research investigating the relationship between specific, maladaptive aspects of perfectionism and social phobia. The Multidimensional Perfectionism Scale (MPS-F; R. O. Frost, P. Marten, C. Lahart, & R. Rosenblate, 1990) was administered to a consecutive series of adult outpatients (N = 61) attending a group-based cognitive–behavioral treatment program for social phobia. MPS-F variables, Concern over Mistakes (CM) and Doubts about Actions (DA), were both associated with social anxiety severity at pretreatment. Despite the theoretical relevance of the CM dimension to social anxiety, the relationship between these two constructs did not remain significant once neuroticism and depression were controlled. Contrary to predictions, CM failed to predict treatment outcome beyond pretreatment social anxiety. Results are discussed in terms of the overlap between perfectionistic concern about mistakes and fear of negative evaluation in social phobia.