Achromobacter xylosoxidans (formerly Alcaligenes xylosoxidans) is a rare but important nosocomial pathogen. Antibiotic resistance has been increasing during the past decade. A. xylosoxidans may be confused with Pseudomonas spp. but, unlike Pseudomonas spp., this organism has peritrichous flagella. Complicated intra-abdominal infection with A. xylosoxidans has rarely been reported in the literature. This report is of an immunocompetent patient with acute cholecystitis complicated by an intra-abdominal abscess after surgery. Culture of both blood and ascites yielded extended drug-resistant A. xylosoxidans, which was only sensitive to colistin. The clinical and laboratory characteristics of A. xylosoxidans are presented.