As a part of the conference ITAT 2018, the 6th international workshop “Computational Intelligence and Data Mining” has been organized. It is aimed at participants with research interests in any of these related areas, especially at PhD students and postdocs. Interested participants were invited to submit a paper in English of up to 8 double-column pages, prepared according to the instructions at the ITAT 2018 web pages. As this workshop started, 5 years ago, it had only 7 regular submissions. However, the interest in the computational intelligence and data mining workshops has been gradueally incereasing since that time. This year, we have 1 invited talk by internationally renowned expert Filip Šroubek, and 12 regular papers had been submitted to the workshop, among which 11 have been accepted for oral presentations and for inclusion in these proceedings. A key factor influencing the overall quality of a workshop and of the final versions of the submitted papers is the workshop's program committee. The 6th international workshop “Computational Intelligence and Data Mining” is grateful to the 27 reviewers from 11 countries who read the submitted papers, and have provided competent, and in most cases very detailed, feedback to their authors. Most of them have a great international reputation witnessed by hundreds of WOS citations.