Two persons, identified as Brijmohan and Golu, have been arrested while the third accused was still at large, they said.
The woman, a resident of West Delhi's Baljeet Nagar area, had come to RML hospital last evening along with a relative for his check up.
They were walking through Ridge Road on their way to home. The woman asked her relative to stop at one point answer nature's call.
"In the meantime, three men reached the spot. They allegedly threatened and overpowered the two. While two of them took the woman in the bush on the roadside and raped her, the third kept a tab on her relative. They then robbed the duo and fled from the spot," said a police official.
She was taken for medical examination which confirmed rape, police said.
A case of gang rape and robbery has been registered at Mandir Marg police station and two accused have been arrested while efforts were on to nab the third, they said.