The Gonococcal Isolate Surveillance Project is a national sentinel surveillance system to estimate levels and monitor trends of antimicrobial resistance in prospectively collected isolates of Neisseria gonorrhoeae. Of 6204 isolates evaluated from 21 clinic sites between September 1987 and December 1988, 21% met at least one of the surveillance criteria for resistance to penicillin, tetracycline, cefoxitin, or spectinomycin; 2.2% were penicillinase-producing N gonorrhoeae; 1.0% had high-level plasmid-mediated tetracycline resistance; and 16.8% of the isolates without plasmid-mediated resistance had chromosomally mediated resistance (defined as a minimum inhibitory concentration greater than or equal to 2 micrograms/mL) to penicillin, tetracycline, or cefoxitin. Three isolates were resistant to spectinomycin. All isolates were susceptible to ceftriaxone. Resistant isolates were identified from all participating centers. Patient demographic and behavioral characteristics were not predictive of infections caused by resistant organisms. These results demonstrate the wide distribution of antimicrobial-resistant N gonorrhoeae and support recent changes in Centers for Disease Control therapy recommendations for gonococcal infections that no longer recommend tetracycline and penicillin as first-line therapies.