The Project Management Office (PMO) is a relatively new type of organizational unit, responsible for supervising internal projects. However, PMOs do not always create and deliver the necessary knowledge for the decisional process. This paper proposes a solution to this problem through the literature-based Project Management Office Maturity Model (PMOMM) that evaluates whether if PMO related processes are implemented and supported by technology. PMOMM consists of 30 main project management processes, organized into 7 capability areas. In order to assess the maturity level of a PMO, a maturity assessment questionnaire was developed. Then, 10 case studies were conducted in which the PMOs of the corresponding organizations were evaluated against PMOMM. The results of the analysis were tested for validity and confirmed by the case study respondents. PMOMM received positive feedback from these experts. stating that the PMOMM represents an easy, yet detailed checklist for organizations to determine the current situation of their PMO.