People infected with hepatitis C can be cured with existing treatments, researchers have discovered.
The virus is carried in blood cells
Around 99% of patients successfully treated with pegylated interferon and ribavirin had no detectable virus for up to seven years.
The treatments were known to work initially but it had been unclear whether the virus would come back.
Experts said it was good news for patients but that some still suffer from painful symptoms.
Over the past decade the number of people in the UK diagnosed with hepatitis C has increased because of higher rates of testing.
But many people are still unaware they are carrying the infection.
Hepatitis C, which is contracted through infected blood, can cause cirrhosis, liver failure or cancer.
Early treatment is usually effective.
Professor Mitchell Shiffman, chief of hepatology at the Virginia Commonwealth University Medical School, and colleagues carried out a long-term study in 1,000 patients to find out whether the virus would come back.
Participants were given a course of injections of pegylated interferon alone or in combination with ribavirin.
In those for whom treatment was successful (no detectable virus after six months) only eight patients tested positive for the virus in the following seven years.
The researchers pointed out it had not yet been determined if those patients had suffered a relapse or been reinfected.
Professor Shiffman said: "We are encouraged by this data because it is rare in the treatment of life-threatening viral diseases that we can tell patients they may be cured.
"In hepatitis C today, we are able to help some patients achieve an outcome that effectively enables them to put their disease behind them."
It is believed that around 250,000 people in the UK have signs of hepatitis C infection, although some of these will clear it naturally and not become chronically infected.
However, the number could actually be as high as half a million and it is estimated that nine out of ten people do not know they are infected.
It can take years or even decades for symptoms to appear but a recent Department of Health campaign has been encouraging those at risk to get tested.
Anyone who ever shared equipment for injecting drugs - even if it was a long time ago, and even if they only did it once or twice - they could be at risk from hepatitis C.
Others could have become infected through a blood transfusion, if they received one before screening was introduced in 1991 - or through sharing banknotes or straws to snort cocaine.
Charles Gore, chief executive of the Hepatitis C trust said the results would be reassuring for patients who had to undergo six months to a year of weekly injections and daily tablets.
"This data looks incredibly promising and it's extremely good news for patients as they are always concerned that the virus would come back."
"The only thing we would add is that we're talking about a cure for liver disease, which is the thing that kills you, but not everyone feels fantastic at the end of treatment - some people have lingering symptoms such as aches in their joints and feeling tired."