An independent review of ACC, the second in 18 months, has found the number of sex-abuse claims lodged has fallen by 36% since 2008.
The review also found that only 3.6% of sensitive claims were accepted in 2011, down from 60% in 2008, when National took office.
The review says ACC needs to be sure the assessment process is not deterring people from seeking help.
Lawyer John Miller, who specialises in ACC cases, says the fall in claims suggests people have lost confidence in the system.
ACC has acknowledged it has more work to do to implement the recommendations of a review into its handling of sensitive claims.
Claims management general manager Denise Cosgrove acknowledges significant change is needed at the corporation and it is working hard towards that.
She said an 18- month action plan has been agreed on to show what work is needed and what has been implemented.