This could be more efficient (esp if "pkstuff" tight and/or the table is indexed properly for the correlated SELECT):

select CONVERT (varchar(9),EMPLOYEE_ID) AS emp_id

, CONVERT(datetime,(CONVERT(varchar(8),ADMISSION_DTE))) AS Adm_date

, ADMISSION_CDE

, ADMIT_TYPE_CDE

, CONVERT(datetime,(CONVERT(varchar(8),DISC_DTE))) AS Dis_date

, DISC_CDE

, DISC_TYPE_CDE

from CurrentTable ct1

WHERE [BranchID]='950' AND (DISC_DTE IS NULL OR (DISC_DTE > 20120630 AND DISC_DTE < 20130201))

and ct1.admission_dte = (SELECT MAX(ct2.admission_dte) from curenttable ct1 WHERE ct1.pkstuff = ct2.pkstuff)

order by emp_id , adm_date

You can also solve this with this construct: , ROW_NUMBER() OVER(partition by ... order by admission_dte desc) as rownumber

WHERE rownumber = 1