The first multicentre survey of sexually transmitted diseases (STDs) performed in Papua New Guinea was conducted in STD clinics in five towns, Port Moresby, Goroka, Rabaul, Lae and Daru, from September 1989 to May 1990. Infections with Neisseria gonorrhoeae and Chlamydia trachomatis (alone or in combination) were common. Penicillinase-producing N. gonorrhoeae (PPNG) represented 44% of all gonococcal isolates but significant intrinsic resistance to penicillin was not found. Of the other antibiotics tested, significant elevation of minimum inhibitory concentration (MIC) was common only for tetracycline, although no high-level tetracycline resistance was detected. C. trachomatis was detected by direct immunofluorescence (DIF) in 26% of 210 males and 27% of 64 females. 10% (21/210) of males and 11% (7/64) of females were both DIF positive for C. trachomatis and culture positive for N. gonorrhoeae. Of 203 males and 78 females tested, 5% and 12%, respectively, had serological evidence of current syphilis infection. Clinically, genital ulcer disease was most commonly due to syphilis, donovanosis or genital herpes, while specific vaginal infections were commonly seen in female patients attending Port Moresby and Lae STD clinics.