Jingtian  +  953124 Mon, 26 Oct 09 03:37 AM I never use an apostrophe with these abbreviations, unless it would cause confusion without the apostrophe, e.g. when the abbreviation is a combination of uppercase and lowercase letters. So the following plural forms look OK to me: CDs, DVDs, UFOs, PhD's. Jingtian Joined on Sun, Aug 14 2005 Full Member 197 Plurals, Spelling, Punctuation, Abbreviations, Apostrophes