§  720.20  Youthful offender determination; when and how made; procedure
        thereupon.
  1.   Upon  conviction  of  an  eligible  youth, the court must order a
pre-sentence investigation of the defendant.  After receipt of a written
report  of the investigation and at the time of pronouncing sentence the
court must determine whether or not the eligible  youth  is  a  youthful
offender.   Such determination shall be in accordance with the following
criteria:
  (a)   If  in the opinion of the court the interest of justice would be
served by relieving the eligible youth  from  the  onus  of  a  criminal
record and by not imposing an indeterminate term of imprisonment of more
than four years, the court may, in its  discretion,  find  the  eligible
youth is a youthful offender; and
  (b)   Where  the  conviction  is had in a local criminal court and the
eligible youth had not prior to commencement of trial or entry of a plea
of  guilty  been  convicted of a crime or found a youthful offender, the
court must find he is a youthful offender.
  2.   Where  an  eligible  youth is convicted of two or more crimes set
forth in separate counts of an accusatory instrument or set forth in two
or  more  accusatory  instruments  consolidated  for trial purposes, the
court must not find him a youthful offender with  respect  to  any  such
conviction  pursuant  to subdivision one of this section unless it finds
him a youthful offender with respect to all such convictions.
  3.   Upon  determining  that an eligible youth is a youthful offender,
the court must direct that the conviction be deemed vacated and replaced
by  a  youthful  offender  finding;  and  the  court  must  sentence the
defendant pursuant to section 60.02 of the penal law.
  4.   Upon  determining  that  an  eligible  youth  is  not  a youthful
offender, the court must order the accusatory  instrument  unsealed  and
continue the action to judgment pursuant to the ordinary rules governing
criminal prosecutions.

(For recent amendments consult Official Text from Senate Gopher site.)

.