Objectives To determine the impact of legislative changes to the New South Wales (NSW) workers’ compensation scheme on injured workers access to benefits, insurer claim processing and work disability duration.

Methods Population-based interrupted time series study of workers’ compensation claims made in NSW 2 years before and after legislative amendment in June 2012. Outcomes included incidence of accepted claims per 100 000 workers, the median and 75th percentile insurer decision time in days, and the median and 75th percentile of work disability duration in weeks. Effects were assessed relative to a comparator of seven other Australian workers’ compensation jurisdictions.

Results n=1 069 231 accepted workers’ compensation claims were analysed. Claiming in NSW fell 15.3% following legislative reform, equivalent to 46.6 fewer claims per 100 000 covered workers per month. This effect was greater in time loss claims (17.3%) than medical-only claims (10.3%). Across models, there were consistent trend increases in insurer decision time. Median work disability duration increased following the legislative reform.

Conclusions The observed reduction in access to benefits was consistent with the policy objective of improving the financial sustainability of the compensation scheme. However, this was accompanied by changes in other markers of performance that were unintended, and are suggestive of adverse health consequences of the reform. This study demonstrates the need for care in reform of workers’ compensation scheme policy.