The number of cases of chlamydia in Scotland has risen sharply, according to the latest official statistics.
More testing is thought to have added to the rise in chlamydia cases
Sexual health clinics diagnosed more than 4,800 cases in 2002 compared to 3,500 the year before, a rise of 39%.
Most of those diagnosed with a sexually transmitted infection were in their 20s or early 30s, but one in seven was in their teens.
The figures on infection reported at clinics were compiled by NHS Scotland's Information Services.
The report found that the increase in chlamydia was one of the main trends.
It said: "It has been suggested that some of this is related to increased awareness and to wider application of laboratory tests.
"There is also thought to be a genuine increase in the level of infection, mainly in the 15-24 age group."
A Scottish Executive spokeswoman said much of the increase could be explained by better screening and detection.
"We are actively trying to encourage more people to come for checks," she said.
"The increase means we are succeeding in identifying people who are carrying these diseases and giving them the appropriate treatment."
Scotland's chief medical officer Dr Mac Armstrong said the figures for young people were a "disappointment but not a surprise".
He highlighted a lack of awareness among teenagers of the risk of sexually-transmitted infection.
"Scottish teenagers have just about the lowest condom use of any comparable group of teenagers worldwide," said Dr Armstrong.
"There is clearly a lack of awareness and lack of availability of condoms among teenagers in Scotland and we need to tackle this."
He warned: "We have to get that simple message across to them: practise safe sex, use a condom."
The number of gonorrhoea cases dropped dramatically between 1985 and 1994, but an increase was found in recent years, especially in men.
The main groups of sexually transmitted infections were genital warts, chlamydia, non-specific genital infections and genital herpes simplex.
The average age of people attending clinics was 26, the same as the previous two years.