The twins were born in Gran Canaria
Spanish twins separated at birth 35 years ago through a hospital mix-up are suing the authorities.
The women, who had been brought up in different families, were reunited by chance in 2001.
They were born in a Canary Islands hospital, where one of them was swapped by mistake with another baby girl.
All three women are suing the islands' government. A lawyer for one of the twins said she was seeking 3m euros (£2.4m) in damages.
"It does not take a lot of effort to put yourself in the position of any of these people to understand the damage that has been done," said lawyer Socorro Perdomo.
He said that of the three people most directly affected, his client had suffered the most.
"The first right of any child is the right to their own personal and family identity," he said.
The mistake only came to light when the twins were 28.
Mr Perdomo said a friend of one of the twins was working in a shopping centre in Las Palmas in the island of Gran Canaria.
The other identical twin came in one day to buy clothes, but when the sales assistant tried to greet her with a kiss, the customer refused.
The sales assistant, surprised, called her friend - the other twin - who assured her she had not been in the shop.
The sales assistant then realised she was dealing with twins and arranged for the two women to meet.
DNA tests proved they were identical twins, said Mr Perdomo.
The lawsuit is against the government of the Canary Islands - part of Spain - where the mistake was made in a state hospital in 1973.
Mr Perdomo said his client was taken out of a cot next to that of her twin sister and mistakenly replaced by another baby girl. His client was then raised by the family of that baby.
The non-twin was brought up believing that she was a twin sister.
All of those involved are remaining anonymous.