Uninstalling MacPorts can be a drastic step, and depending on the issue you are experiencing, you may not need to do so. If you are unsure, ask on the macports-users mailing list first.

If you need to uninstall MacPorts, and your port command is functioning, first uninstall all the installed ports by running this command in the Terminal:

$ sudo port -fp uninstall installed

All that will be left in your installation prefix now will be files that were not registered to any port. This includes configuration files, databases, any files which MacPorts renamed in order to allow a forced installation or upgrade, and the base MacPorts software itself. You may wish to save your configuration files (most are in $prefix/etc), databases, or any other unique data by moving it aside.

To remove all remaining traces of MacPorts, run the following command in the Terminal. If you have changed prefix, applications_dir or frameworks_dir from their default values, then replace /opt/local with your prefix, replace /Applications/MacPorts with your applications_dir, and/or add your frameworks_dir to the list, respectively.

$ sudo rm -rf \
        /opt/local \
        /Applications/DarwinPorts \
        /Applications/MacPorts \
        /Library/LaunchDaemons/org.macports.* \
        /Library/Receipts/DarwinPorts*.pkg \
        /Library/Receipts/MacPorts*.pkg \
        /Library/StartupItems/DarwinPortsStartup \
        /Library/Tcl/darwinports1.0 \
        /Library/Tcl/macports1.0 \
        ~/.macports

If you use a shell other than bash (perhaps tcsh), you may need to adjust the above to fit your shell's syntax. Also note that depending on which version of MacPorts you have and which ports you have installed, not all of the above paths will exist on your system. This is OK.