Dark tourism is a topic of increasing interest, but it is poorly understood when considering its significance for mainstream and commercial tourism. This paper investigates the significance of dark tourism in the top ten most visited European tourist cities and proposes a dark tourism index for Europe’s tourism cities. Data was collected from the websites of the cities’ Destination Management Organisations (DMOs) using a content analysis methodology, based on keywords related to dark tourism taken from the research literature in this area. Descriptive statistics were produced and the variance between the frequencies of keywords related to each city was analysed for statistical significance. These results were then used to construct a darkness ranking of the cities. There are significant differences in the extent to which dark tourism products and services are promoted by the DMOs of Europe’s top ten most visited European cities. The ranking of cities by darkness does not correspond to the ranking by visitor numbers, and further qualitative analysis suggests that that the ranking is also independent of the actual presence of dark sites within the destination. This implies that European city DMOs are engaging with the emerging dark tourism market with to varying degrees. The purposive sample of ten cities can be extended in future research to increase the validity of the findings of this paper. A further limitation is the selection of keywords for content analysis, which have been developed following the literature review contained below. Future research could develop an extended list of keywords using a systematic review process. This paper shows that it is possible to create a ranking of tourist cities in terms of their darkness, and that this methodology could be extended to a much larger sample size. This links dark tourism research to the urban tourism literature and also offers possibilities for creating a global ranking that could be used by destinations to judge their success in engaging with the dark tourism market, as well as by tour operators seeking to develop products for the same market. This paper will offer DMO's and others the opportunity to hone their tourism products more effectively in a way which offers a better understanding of tourism, and therefore provides for better management of its issues. Dark tourism is a growing niche area of study, and this paper seeks to provide a framework to better understand supply-side aspects of it.