Although marginalised, they are widely feared. They often turn up at weddings and after the birth of boys to demand large donations for their blessings.
Many people pay up in fear of being cursed or embarrassed - eunuchs often hitch up their saris and reveal their mutilated genitalia outside the homes of those who refuse.
In New Delhi, some eunuchs operate as organised extortion gangs and are so successful that there have been calls for them to be hired as tax collectors to boost revenues.
Their fortunes in India have varied throughout the ages. They are mentioned derisively in the Hindu epic, the Mahabharata, but were influential in the royal household during the Mughal period when they were trusted as courtiers and harem guards.
Many of those living in eunuch communities have been rejected by their families either because they were born with deformed genitalia or were effeminate.
Some of them have had distressing and dangerous village castrations to become hijras.
In its ruling, the Supreme Court said the Indian constitution provides equal opportunity "irrespective of caste, religion or gender".
Justice K S Radhakrishnan said the "recognition of transgender (people) as a third gender is not a social or medical issue but a human rights issue".
The court ordered the government to instigate public awareness campaigns to end the stigma suffered by transgenders.