In UK, diagnoses of new sex infections rose by 2% to 376,508 from 2005 to 2006, largely among young people and gay men, the Health Protection Agency (HPA) said.
The biggest rise was seen in genital herpes, up 9% to 21,698. Among girls aged 16-19 the rise was 16%.
Sexual infection diagnoses have been almost continually rising since the 1990s, with the highest increases in recent years being seen in the 16 to 24 age group.
The HPA said part of the rise in the number of people being diagnosed was due to more people coming forward for testing.
During 2006, nearly 1 million people were screened for an STI at a genitourinary medicine (GUM) clinic.
It is also noted that there were encouraging early signs of reversing trends - gonorrhoea and syphilis dropped by 1%.
Professor Pat Troop, chief executive of the Health Protection Agency, said: "There is mixed news in these figures.
"Some infections now appear to be slowing down. But there is no room for complacency.
"The picture for young people remains particularly worrying."
Dr Gwenda Hughes, head of the STI section at the HPA, said higher STI rates were found in young people because they were more sexually active.
Multiple partners, changing partners and failing to wear condoms all contributed to higher rates in this group, she said.
Another group at higher risk is gay men, according to the HPA.
"It's crucial that we reach these groups with messages about safe sex, including condom wearing, and the importance of getting tested if they feel they've put themselves at risk of contracting an STI," said Dr Hughes.
Lisa Power of the Terrence Higgins Trust said: "Many STIs show continued increases, particularly amongst young people and gay men. We have to reverse this trend.
"Quality sex and relationships education - not just biology lessons - has been shown to decrease risky behaviour in teens. We also need to stop the decline in health promotion work for gay men at a local level."
About the rise in genital herpes, she said: "We need to get the message across that this is a lifelong and unpleasant condition which will require ongoing treatment, and not something to be taken lightly."
Anne Weyman of the Family Planning Association said it was important for people to realise that they could catch genital herpes from oral sex as well as unprotected intercourse.