This report describes a study which was carried out to investigate an epidemic of gonococci with resistance to penicillin and tetracyclin (TRNG/PPNG). This study involved all PPNG-isolates which were sent in by five laboratories from Amsterdam, Rotterdam and The Hague in 1989-1990. The epidemic of TRNG/PPNG was found to be related mainly to three strains: NR/IB-6, PRO/IA-3, PRO/IA-6 with the plasmid pattern 3.2+25.2. The introduction of TRNG/PPNG presumably took place in The Hague in 1988. Independent risk factors of an infection due to TRNG/PPNG were for men: age above 40 years, and sexual contact with a prostitute (only for men in Rotterdam and The Hague). No relation with prostitution was found for men in Amsterdam. Independent risk factors were for women: age above 40 years and Turkish or Latin American nationality. Strains from The Hague were also independently correlated to TRNG/PPNG. Further spread of resistant strains seems to be related to prostitution, but only in Rotterdam and The Hague. The outbreak of TRNG/PPNG underlined the necessity for a continuous surveillance of resistance of gonococci including some background variables of patients.<br>