What is the plural possessive noun of MD?

Answer 1

There are two accepted forms of making an acronym into a plural form:

1. add an apostrophe s ('s) at the end, MD's
2. add a lower case s at the end, MDs

As you can see, the first example will not work when you also want a plural acronym in the possessive form. I always prefer the second example for the plural of an acronym.

The possessive form of example 2 is MDs'. Of course, you can never go wrong if you spell out the acronym: Medical Doctors'.

Note: I deliberately described the form MD as an acronym rather than an abbreviation because abbreviations can be so varied (i.e., cont., n.) and clumsy to make plural or possessive. It is always proper to spell out an abbreviation when it is more than a notation.