Is post traumatic one word, two words, or - nated?

[SithSolo1]

As in post traumatic stress. I've seen it all 3 ways

 

[goog]

I've seen it all three ways as well, don't think it really matters.
For the record it is one word at dictionary.com.

 

[amnesiac]

PTSD can be spelled any of the three common ways (post-traumatic, posttraumatic, post traumatic). They are all correct. DSM-IV seems to prefer posttraumatic, for the record.