 In 1998, she co-authored "Fedsure Life Assurance Ltd v Greater Johannesburg Transitional Metropolitan Council", the Court's founding judgment on the rule of law and legality review.The first major judgment of which she was the sole author was "Premier, Mpumalanga", still the leading authority on the doctrine of legitimate expectations (on which O'Regan also wrote in "Ed-U-College", again in the context of the government's withdrawal of school subsidies).O'Regan's judgment in "Dawood v Minister of Home Affairs", delivered in 2000, established for the first time that the right to family life is constitutionally protected and that the conferral of broad discretionary powers on government officials can be unconstitutional.