We performed a cross-sectional study at an outpatient AIDS clinic to assess the prevalence of Campylobacter species in stool specimens from 201 consecutive patients infected with human immunodeficiency virus (HIV). We characterized campylobacters phenotypically and genetically by using primers for the group of common species (i.e., C. jejuni, C. coli, C. lari, and C. upsaliensis) and for most individual uncommon species. We performed cultures with use of a membrane filter technique on nonselective blood agar and found that Campylobacter species were the most frequent enteropathogenic bacteria: the organisms were recovered from 7 (16%) of 43 patients with diarrhea and 5 (3%) of 158 patients without diarrhea (P = .001). We isolated only one campylobacter with use of conventional culture techniques on selective media. Phenotypic characterization of 10 campylobacter strains resulted in the misidentification of four isolates. C. upsaliensis was the most frequently isolated species, followed by C. jejuni and C. coli. Two strains could not be identified with the available primers. Two of 12 Campylobacter strains were resistant to erythromycin, and two were resistant to ciprofloxacin. We conclude that Campylobacter species other than C. jejuni can frequently be detected in the stools of HIV-infected patients and that these organisms could be associated with diarrhea.