This paper presents the findings of a survey on the use of UML in software maintenance, carried out with 178 professionals working on software maintenance projects in 12 different countries. As part of long-term research we are carrying out to investigate the benefits of using UML in software maintenance, the main objectives of this survey are: 1) to explore whether UML diagrams are being used in software industry maintenance projects; 2) to see what UML diagrams are the most effective for software maintenance; 3) to find out what the perceived benefits of using UML diagrams are; and 4) to contextualize the kind of companies that use UML documentation in software maintenance. Some complementary results based on the way the documentation is used (whether it is UML-based or not) during software maintenance are also presented