A SEXUALLY active person can be carrying chlamydia without any symptoms for years until it comes time to reproduce, and that's when they discover they are infertile.

If only they knew a simple urine test, a couple of pills and a condom could make it all go away or stop the infection in the first place.

This year's Sexual Health Week theme - Check it Out - is targeted at 16-25-year-olds, the biggest risk group for the disease.

chlamydia transmission is still the most commonly reported sexually transmitted infection (STI) in NSW.

Since 2006, chlamydia notifications in NSW have risen from 12,015 to 20,469 in 2011, with about 60% of notifications in 2011 in the 15-to-25-year age range.

The advice for young people who are sexually active is to visit their doctor regularly to test for sexually transmissible infections and, in particular, chlamydia.

The Northern NSW Local Health District's sexual health staff specialist, Dr Natalie Edmiston, said chlamydia was very common among young people aged under 25.

"If you are sexually active, use condoms and water-based lubricant and see a doctor for a sexual health check-up."

Dr Edmiston said all sexually active young people should consider asking their GP for a chlamydia test at least once a year.

Alternatively, the sexual health clinic at Grafton Base Hospital offers free and confidential sexual health checks for everyone from 8am-4.30pm Monday to Friday.

 As a special offer for Sexual Health Week, the clinic has 50 fun-safe sex packs to give away, each containing a flavoured condom, lubricant, information and a tin carry pack.