In this study we attempt to understand why formal evaluations of IT investment projects have not yet become an organizational routine. Using survey data gathered from business and IT managers in Sweden, we tested the research hypotheses about the factors influencing the attitudes and behaviour of managers towards using formal evaluation methods based on the theory of planned behaviour. We found that the intent to use formal evaluation methods in an organization is determined by the attitudes of the managers towards the formal methods, the common beliefs of the organization about the formal methods, and the perceived ability to perform formal evaluations. Interestingly, we found that the attitudes toward formal methods are determined mostly by the perceived usefulness of the methods and not by the perceived ease of use of these methods, suggesting that the decision to use formal methods is most likely based on rational analyses rather than individual preferences. We also found that awareness and selfefficacy contribute to the use of formal methods via influences on organizational beliefs and perceived ability to perform evaluation tasks. These findings provide some interesting managerial implications for advocating the use of formal methods in organizations.