Former premier Morris Iemma's gift to Sydney, the high profile World Youth Day that was held in July, ran $100 million over budget.

As a result, the NSW Auditor-General is calling on the Government to undertake a full review of the event, so it can more accurately plan for future large-scale events held in the state.

"The estimated final cost for World Youth Day is six times the original budget estimate," NSW Auditor-General Peter Acherstraat said in a report released today.