Tiny two feet tall Jyoti Amge, from Nagpur, India, celebrated the occasion with a birthday cake almost as big as her.
Already widely regarded as the world's smallest girl, Jyoti is anxiously waiting for official confirmation that she has grabbed the adult title from 2ft, 3in American record holder, Bridgette Jordan.
"It has been my dream to be recognised as the world's smallest woman for many years, but I have had to wait for my 18th birthday," says Jyoti.
"Today I became a woman so I hope don't have to wait much longer."
Jyoti, who at just 11lbs (5 kg) is half the weight of her two-a-half-year-old neighbour, has a form of dwarfism called achondroplasia, meaning she stopped growing shortly after her first birthday.
Despite this she insists on being treated like any other young woman and likes nothing better than doing her make up and going clothes shopping with her friends - the only difference being that due to her tiny legs she doesn't mind being picked up and carried.
"I do my make up just like taller girls and I shop along with my sisters, buy clothes with my mother and father - I do everything according to my wishes," explains Jyoti.
"The biggest problem I have is that my hair is longer than me so I need help in making my hair."
Due to her size, Jyoti has to have clothes and jewellery made for her. She sleeps in a tiny bed and uses special plates and cutlery to eat, as normal-sized utensils are too big.
She's so small she even fits perfectly inside the basket on her sister's bicycle when she needs to be taken around town.
"The advantage of being short is that wherever I go people get attracted towards me and let me go first," says Jyoti.
"I can go wherever I want, no one stops me going anywhere. When I go out crowds gather and wonder how a girl so short does so many things."
With dreams of stardom, Jyoti has already featured in a music video for Indian Bhangra-rap star Mika Singh, TV shows across the world and an hour-long National Geographic documentary on her life. Bollywood has also come calling, with two films lined up for the budding actress next year:
"I wish that my wax statue should be made at Madam Tussauds museum in London. I would be glad if that happened.
"I like being famous and want to be an actress to make other people happy."
Despite her increasing fame, Jyoti's family are her future. Growth problems have left her bones so brittle they are in danger of breaking in a simple fall.
She is likely to need care for the rest of her life and older sister Archana, 26, admits she is likely to have to care for Jyoti as her parents get older.
"I will only marry a person who Jyoti likes," says Archana.
"Even when someone is interested I ask Jyoti if she likes him. I will treat her like I have since childhood and I would never like to be separated from her."