The American Medical Association (AMA) Style is included with the installation of EndNote. It can be located in EndNote under “JAMA” for Journal of the American Medical Association. In EndNote, click on the Edit menu > Output Styles > Open Style Manager. Browse to the end of the Styles with the letter J to locate the JAMA style. You can check the box to the left of the Style name to mark this as a favorite and then close the Style Manager. The JAMA style will now be available to use.
You can also download the JAMA style here:
http://endnote.com/downloads/styles
The installation instructions can be found in http://endnote.com/kb/106495