The major objective of this study was to extract and test the most important elements of management information systems (MIS), and to empirically determine critical success factors (CSF) for MIS rightsizing success. The research model was based on Rockart’s classic 1982 study of CSF as modified by Martin’s 1982 study and more recent literature. Questionnaires were mailed to MIS managers from selected U. S. companies. MIS managers were randomly selected from a purchased database. Data had been collected and statistically analyzed. Six sets of hypotheses were tested and significantly supported by the statistical results. The canonical correlation were significant for each hypothesis. Eighty percent of the variance of MIS rightsizing success can be explained by the particular MIS rightsizing activities. The canonical correlation analysis identify the six CSF: user appreciation and involvement, communication and facilitation of MIS department to users, support services of the MIS department, the commitment and support from top management and users, organizational effectiveness, and the appropriate software, were significantly important to MIS rightsizing success.