"Light It Up Blue" is an initiative by the social justice and empowerment -- blue being the official symbolic colour for autism.
Historical monuments including Red Fort, Humayun's Tomb, Safdarjung Tomb, Purana Quila, Jantar Mantar and Qutab Minar were lit up in blue lights.
At the same time, an event was held at Humayun's Tomb, with participation of several autistic children from the city.
A book titled "Why Me?" and a song - "Alag Si Asha" were unveiled by Social Justice and Empowerment Minister Kumari Selja.
Autism is a neuro-physiological disorder which affects the social and emotional areas of the brain.
According to the National Trust - a body under the ministry, working for people affected with autism, cerebral palsy, mental retardation and multiple disabilities, autism affects as many as one in 110 children and one in 70 boys and boys are four times more likely than girls to have autism.
Though, there is no medical cure for autism, early diagnosis and intervention can help people to adapt and function better.
The UN General Assembly declared April 2 as WorldAutism Awareness Day, to be observed every year since 2008.
Several other events were organized in the city Tuesday while public messages were published by the National Trust in leading dailies to highlight autism.
An 'Autism Awareness Walk 2013' was organized Tuesday morning at India Gate and several school children participated in it.
Image: Humayun's Tomb is lit up in blue to mark World Autism Day in New Delhi, Tuesday, April 2, 2013. (AP)