Congress actions represent a specific part of the hotel services market. In conditions of the hotel trade development in the last decade congresses mean a distinguished component of the hotel incomes. However, this very market segment has been eminently influenced by the entire development of the economical environment after 2008. That is why the main objective of this contribution is to find out - with usage of diffusion analysis of the 2009 – 2015 time series - whether there exists any statistically conclusive difference between average number of conferences in mass accommodation facilities in the Czech Republic for the categories of region and type of hotel. For the computation, the level of importance alpha = 0,05 has been set up. Also, there has been made the analysis for number of conferees. Further objective was to find out - using correlation of time series variation from trend for the variables number of conferences and number of conferees - whether it is possible to consider changes of number of conferences as a cause of change of number of their visitors. The results obtained are related to the development of hotel services market in the Czech Republic in the period in view.