How do I get a list of what Patients exist in VistA ?

There are several ways to find out what Patients exist in VistA.

A simple way is to use VA FileMan:

Select OPTION: PRINT FILE ENTRIES  

OUTPUT FROM WHAT FILE: INSTALL// 2  PATIENT  (359461 entries)
SORT BY: NAME// 
START WITH NAME: FIRST// 
FIRST PRINT FIELD: NUMBER
THEN PRINT FIELD: NAME
     1   NAME  
     2   NAME COMPONENTS  
CHOOSE 1-2: 1  NAME
THEN PRINT FIELD: 
Heading (S/C): PATIENT LIST// 
DEVICE: HOME  GENERIC TELNET TERMINAL    Right Margin: 80// 
PATIENT LIST                                   AUG 18,2009  11:11    PAGE 1
NUMBER        NAME
 ---------------------------------------------------------------------------
256807        ANDREWS,ARCHIE
220870        BECK,BLUTO
397624        BECK,BRUTUS
111345        BOOP,BETTY
348052        DUCK,DAISY
179792        DUCK,DONALD
264262        MOUSE,MICKEY
140335        PEA,SWEET
124961        OYL,OLIVE
2515          THE SAILOR,POPEYE