dealing with duplicates on a daily basis, i find this approach works well

alter table withdupes add delid int identity(1,1)

delete x

from withdupes x

inner join (

select itemno, min(delid) as keepid

from withdupes

group by itemno

) y on x.itemo = y.itemno

where x.delid <> y.keepid

alter table withdupes drop column delid