Web Content Management Systems (CMS) are traditionally used in institutions to allow web content management by people without technical skills. This study intends to check the influence of the CMS in the accessibility of the contents they handle. First, an accessibility analysis of six widely used CMS is performed base don the Authoring Tool Accessibility Guidelines (ATAG). Second, an accessibility analysis of a series of city council web pages managed by abovementioned CMS by using Web Content Accessibility Guidelines (WCAG). Results of the study show that although web pages managed by the CMS with a better degree of ATAG fulfilment provide better accessibility, there is no direct correlation between results obtained in both evaluations. Information about what aspects cause accessibility errors in the CMS and the impact of such aspects in accessible web content management is also provided.