I'm wondering whether slf4j/logback (potentially) suffers from the same problems as log4j: http://www.mail-archive.com/log4j-user@logging.apache.org/msg11921.html http://www.mail-archive.com/log4j-dev@logging.apache.org/msg11378.html I'd switch from slf4j/log4j to slf4j/logback if this solved the issue. [Abstract] If you don't want to go through the above referenced posts... According to Tomcat's (>=6.0.24) "memory leak detection" listener the log4j MDC has a memory leak: "A web application created a ThreadLocal with key of type (...) and a value of type (...) but failed to remove it when the web application was stopped." That's because log4j doesn't provide something like ThreadLocal#remove. Regards, Marcel -- Marcel Stör, http://www.frightanic.com Couchsurfing: http://www.couchsurfing.com/people/marcelstoer O< ascii ribbon campaign - stop html mail - www.asciiribbon.org