The Police Ombudsman launched an inquiry after a complaint was made that police did not fully investigated claims against the Sinn FÃ©in president.
A police probe into the allegations was conducted properly, it said.
The ombudsman, Dr Michael Maguire, said there were no signs of misconduct.
He also said he had "found no evidence to indicate that [police officers'] thinking was influenced by who Mr Adams was".
The complaint was in relation to Mr Adams' evidence in the case of his brother, Liam.
Liam Adams was convicted in 2013 of raping his daughter, Ã

From 1 January cars and motor caravans will pay £6.70 - up 10p - while tolls for small goods vehicles and small buses will rise by 20p to £13.40.
Severn River Crossing raises the prices each year in line with inflation.
Labour MP Jessica Morden said the toll was now nearing the minimum wage, but UK ministers plan to halve the tolls in 2018.
Prices for heavy goods vehicles and buses will rise by 20p to £20.
The average increase is 1.3%, according to the operating company Severn River Crossing plc.
The Severn Bridges Act 1992 allows for the tolls to be amended annually with the agreement of the UK Department for Transport.
Ms Morden, who is MP for Newport East, said: "For many of my constituents on the Tories' minimum wage, the cost of travelling across the bridge is now almost equivalent to an hour's pay, and is actually above it for people under 21.
"That means they are effectively losing an hour's pay every day that they cross the bridge."
The government's National Living Wage is currently £7.20, while the minimum wage is £6.95 for 21 to 24-year-olds and £5.55 for 18 to 20-year-olds.
Ms Morden added that the UK government had yet to explain what its plans were for when the bridges return to public ownership - expected around 2018.
"All we know is that the government have announced that the tolls will come down next year when the contract comes to an end, but there is still no sign of the public consultation that was promised," she said.
Labour's Shadow Welsh Secretary Jo Stevens said: "With these higher toll costs about to hit people who are already having to tighten their belts, we now need absolute certainty from the UK government about what exactly is going to happen."
In March, the then Chancellor George Osborne announced in his budget that the toll charges would be halved in 2018, when the bridges were expected to have been returned to UK government ownership.
Welsh MPs were told by Transport Minister Andrew Jones in July that the switch may come as early as October 2017.
Mr Jones said tolls may still be charged to cover maintenance, but added: "They are not a cash system... to fund a scheme in Kent or a scheme somewhere else."
In November, assembly members from all four party groups backed a call to scrap the tolls, condemned by UKIP AM Mark Reckless as a "tax on Wales".
However, Labour backbencher Lee Waters argued that the tolls should be kept and used to fund the South Wales Metro project to boost public transport.
A UK government spokesman said it had "announced its intention to halve the tolls on the River Severn Crossings".
"We will launch a consultation on the Severn Bridge and confirm further details in due course," he added.
A recommendation not to prosecute Gerry Adams over allegations he withheld information on sexual abuse within his family was not politically motivated, a police watchdog has found.
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Tolls to cross the Severn Bridge and Second Severn Crossing into Wales will increase in the New Year.