While the field of data mining has been studied extensively, most of the work has concentrated on discovery of patterns. Outlier detection is currently very active area of research and finding outliers in a collection of patterns is a very well-known problem in the data mining field. An outlier is a pattern which is dissimilar with respect to the rest of the patterns in the dataset. Depending upon the application domain, outliers are of particular interest. In some cases presence of outliers are adversely affect the conclusions drawn out of the analysis and hence need to be eliminated beforehand.