Scope is on target to ensure that disabled people make up 20 per cent of its workforce by 2007.
The charity says this is partly because existing employees are declaring their disabilities for the first time.
Two years ago, only 93 of Scope's 4,000-strong workforce, or 3.7 per cent, were disabled. It set itself a target of 20 per cent to reflect the number of people in the UK workforce who are disabled.
Since the charity introduced a 'reserved posts' policy for instances where it felt the job would be performed better by a disabled person, the proportion of disabled employees has risen to 17.2 per cent.
But Andy Rickell, executive director of diversity politics and planning at Scope, said the increase was not occurring only because the charity was taking on new disabled staff. A total of 393 people already working at the charity have declared themselves disabled after not doing so previously.
"People who were already working at Scope have been willing to declare that they have an impairment for the first time," Rickell said. "They are no longer worried about being discriminated against because of it.
"We are talking about people who chose to hide their impairments out of fear that it might hold back their careers. But we have created an environment in which people know that we positively encourage members of the disabled community to work for us."
A spokesman added that the charity now includes both dyslexia and diabetes as impairments.