AbstractThe aim of this study was to investigate the effect of chronic Alcaligenes species infection of the respiratory tract on the clinical status of patients with cystic fibrosis. We conducted a retrospective case‐controlled study. The microbiological records of all patients attending the Leeds Regional Pediatric and Adult Cystic Fibrosis Units from 1992–1999 were examined. Chronic Alcaligenes infection was defined as a positive sputum culture on at least three occasions over a 6‐month period. These patients were compared with controls matched for age, gender, respiratory function, and Pseudomonas aeruginosa infection status. Respiratory function tests, anthropometric data, Shwachman‐Kulczycki score, Northern chest x‐ray score, intravenous and nebulized antibiotic treatment, and corticosteroid treatment were compared from 2 years before to 2 years after Alcaligenes infection.From a clinic population of 557, 13 (2.3%) fulfilled the criteria for chronic infection. The median age at acquisition of infection was 17.2 years (range, 6.5–33.6). There was no significant difference in the changes of percentage predicted values for FEV1, FVC, FEF25–75, or Shwachman‐Kulczycki and Northern chest x‐ray scores, or in weight, height, and body mass index z‐scores between Alcaligenes‐infected cases and controls. There was also no significant difference in the use of antibiotics (intravenous and nebulized) or corticosteroids (inhaled and oral).We conclude that in our clinic, chronic infection with Alcaligenes species was uncommon. Chronically infected patients showed no excess deterioration in clinical or pulmonary function status from 2 years before to 2 years after primary acquisition. Pediatr Pulmonol. 2002; 34:101–104. © 2002 Wiley‐Liss, Inc.