In a qualitative research approach, an interpretive case study has been conducted. 26 experts from a large financial service provider of the cooperative banking sector were interviewed. The impact of organizational culture on the management of an organization’s IT project portfolio was subject to inquiry. We have identified three core dimensions of the organizational culture of the analyzed bank: ‘safeguarding culture’, ‘consensus orientation’, and ‘sustainability orientation’. These three central cultural elements influenced the company’s project portfolio management in a way that the portfolio of projects was oversized, resulting in a shortage of key IT resources in individual projects. As a cultural issue, the organization placed more emphasis on a sustainable, long-term oriented, effective project portfolio, rather than on efficient single IT project performance.