The Work and Pensions Secretary was speaking as disability living allowance (DLA) begins to be replaced by the personal independence payment (PIP), which charities say will remove support from many in real need.
Reforms to disability benefits will end the "ridiculous" system that gives people lifetime awards, Iain Duncan Smith has claimed.
Mr Duncan Smith said claims in disability benefit have more than doubled in some parts of the country ahead of the changes.
His comments came as nearly half a million people have called on the Tory Cabinet minister to live off £53 a week for a year in a petition being delivered to his office on Monday.
"Seventy per cent of people on it have lifetime awards which means no one sees you ever again. It doesn't matter if you get better or your condition worsens - it's quite ridiculous," Mr Duncan Smith told the Daily Mail.
"We've seen a rise in the run-up to PIP. And you know why? They know PIP has a health check. They want to get in early, get ahead of it. It's a case of 'get your claim in early'."
He added that rigorous new health checks for claimants were "common sense".
It is the latest in a series of radical welfare changes which started on Saturday, when working-age benefits and tax credits were cut in real terms with the first of three years of maximum 1% rises - well below the present rate of inflation. Trials will also begin this month in four London boroughs of a £500-a-week cap on any household's benefits and of the new Universal Credit system.
Protesters, angry at sweeping welfare reforms and the minister's claim he could live off £53 a day if he had to, will deliver a petition bearing 450,000 names to the Department for Work and Pensions at 10.15am. Mr Duncan Smith has already dismissed the petition as "a complete stunt".
Musician and part-time shop worker Dominic Aversano, from Twickenham, near London, started the petition on campaigning website Change.org. He will deliver the petition to Caxton House in Tothill Street with disability campaigners who say they are at the sharp end of welfare reforms. Mr Aversano, 28, said: "When I started this petition I never imagined the level of support it would get, and the amount of encouragement people would give me. It has sent a powerful message to this Government, showing the level of opposition to their vicious welfare cuts."