The High Court says the Health Ministry acted unlawfully in refusing to consider an application for funding by a woman for looking after her adult disabled son.
The decision on Friday is the latest development in the long-running row over payments for family members looking after adult disabled children.
The judicial review decision concerns Auckland woman Margaret Spencer, whose adult son Paul is seriously disabled with Down's Syndrome.
It follows legal action by other parents who successfully challenged the ministry over the issue, sparking a controversial new policy, which came into effect this month.
After that ruling, Mrs Spencer applied again for funding from the ministry.
The decision on Friday says the ministry acted unlawfully and in breach of Mrs Spencer's rights by refusing to consider this.
It also says she should be able to join the wider group in a future bid for compensation over the matter.
The ministry says it's reviewing the ruling.
Law professor Andrew Geddis says the ruling about payment for those caring for adult disabled children is important but will have a strictly limited effect.
He says the new ruling will not open the door to more legal action because legislation introduced in May means only Mrs Spencer and the nine other claimants are exempt from a prohibition on any future legal challenges.
"The Government has passed new laws, passed new legislation and closed off any avenue to challenge to those laws - so for the people who aren't Mrs Spencer, well, tough."
But Frances Joychild who is the barrister for the group that sparked the claim says the court ruling may open the door for more people to seek compensation for past care of their adult disabled children.