This paper presents the design of a tool for recurring quantitative self-assessment of IT Service Management (ITSM) process maturity in an agile environment. Continual improvement of ITSM processes can be measured by performing a process maturity assessment, comparing the organization’s process performance against a best-practice reference set of processes. In this paper we report a project that has developed a quantitative measuring survey-based tool. The specific context for the research is a financial institution that has adopted agile development. This change brought on an increased need to monitor ITSM process performance, and a Design Science Research (DSR) project was launched to create an ITSM maturity assessment tool. The results show that a company-wide ITSM process maturity assessment can be established as a survey-based self-assessment, and that the aggregate scores from this self-assessment present a good indicator of the organization’s process performance, especially when complemented by a reference score. A key learning from the study is that the iterative DSR methodology made it possible to create a system that in good way measure ITSM process maturity.