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 the VA FileMan Print Option:

Select OPTION: PRINT FILE ENTRIES  

OUTPUT FROM WHAT FILE: INSTALL// 2  PATIENT  (10391321 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,ARCHIBALD
220870        BECK,BLUTO
397624        BECK,BRUTUS
111345        BOOP,BETTY
430565        COOPER,ELIZABETH
123456        DOILEY,DILTON
348052        DUCK,DAISY
179792        DUCK,DONALD
238124        LAKE,VERONICA
223151        KENT,CLARK
823912        MANTLE,REGINALD
293151        MASON,MARMADUKE
264262        MOUSE,MICKEY
519465        OYL,CASTOR
124961        OYL,OLIVE
232311        PARKER,PETER
140335        PEA,SWEET
823111        PRINCE,DIANA
223415        JONES III,FORSYTHE PENDLETON
132515        SAILOR,POPEYE
239123        TATE,POP
231999        WEATHERBEE,WALDO
349582        WAYNE,BRUCE