I am trying to determine the difference between dates for survdate and HIVdate using SAS date values. The format for the variable HIVTSTD2 is MMYYYY and I added the date "15" to all observations so it was in the DDMMYYYY format.  When I run this code below, this is the error statement that I receive: 662  put hivdate= hivdate ddmmyy10.;                           ---------                           48 ERROR 48-59: The format $DDMMYY was not found or could not be loaded. Code: data work0607; set work06 work07; survdate=mdy(imonth,iday,iyear); put survdate= survdate ddmmyy10.; HIVday=15; HIVdate=cat(hivday, HIVTSTD2); *merge the date 15 with all MMYYYY observations found in HIVTSTD2; put hivdate= hivdate ddmmyy10.; if hivdate=15 then hivdate=.; duration = YRDIF(hivdate,survdate,'actual'); run; I appreciate any assistance with this. -Claire ... View more