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