Questions are being asked over exactly how useful a register of child sex offenders would be.

LISTEN ABOVE: Chief Executive of Child Matters Anthea Simcock joins Rachel Smalley on the KPMG Early Edition to discuss the child sex offender's register.

Social Development Minister Anne Tolley has introduced a bill to make a database of all sex offenders over the age of 18.

Otago University Dean of Law Mark Henaghan said it doesn't actually help discourage repeat offending.

He said all the register tells you is where people live, and we'd be better off putting the 35 million dollars into treatment programmes.

"$35 million is a major spend on putting something on a registrar..all it really tells you is where people live and that and it does infringe their rights, we'd be better invested putting that money into treatment programmes."

He said it could breach offenders rights.

 "We're isolating one particular type of offender - child sexual offenders and saying we'll treat them totally different to any other offender who gets released from jail."