reverse dns

[Brad]

Just a quick question.....
  With DNS, for a reverse lookup to work, must there be an entry in the
normal zone file for the host/s before the reverse lookup will work? Whats
say I just add an entry to an IP address I have, in the reverse zone, but
have not assigned it anything in my normal zone file. Will the reverse still
work with that?? Maybe a silly question, but I just been wondering about it
all night hehe
Brad