A total of 19 permethylated derivatives of substituted [CB11H12](-) anions have been prepared using alkylation with microwave assistance. The reactions proceed much faster and more cleanly than under ordinary conditions. Microwave assistance is especially convenient for the permethylation of carborane anions carrying electron-withdrawing groups in positions 1 and/or 12. Even [1-F-CB11H11](-) can be undecamethylated, whereas under ordinary heating, it has only been hexamethylated.