A federal judge has sentenced Dennis Hastert to 15 months in prison, calling the former House Speaker "a serial child molester" who tried to cover up his abuse with hush money.

Using a wheelchair, Hastert, 74, told the court he was "deeply ashamed" that he "mistreated" students while he worked as a school coach in the 1970s.

One of the victims said the abuse left him "devastated" and "betrayed".

Hastert served as an Illinois congressman from 1987 to 2007.

He was the longest serving Republican House Speaker in US history. As House Speaker, Hastert was second in the line of succession to the presidency.

Many of his former Republican colleagues had appealed to the judge for leniency.

In October, he pleaded guilty to violating banking reporting laws after he tried to pay someone $3.5 million to keep quiet about his past sexual abuse.

Prosecutors allege Hastert abused five boys while he was working in Yorkville, a suburb of Chicago, between 1965 and 1981.

However, Hastert could not be charged with the sexual abuse of his victims because of the amount of time that has passed since the crimes.

His defence lawyers had sought to avoid a prison sentence, saying Hastert is in poor health and had already paid a high price in disgrace.

After his guilty plea, Hastert's portrait was removed from the House of Representatives in the US Congress.

Judge Thomas Durkin said on Wednesday that Hastert must also undergo sex offender treatment, serve two years of probation after his release and pay $250,000 to a fund for victims.