Chronic granulomatous disease (CGD) is a primary immunodeficiency due to absent or decreased NADPH oxidase activity in phagocytic cells. The X-linked form of the disease (X-CGD) arises from mutations in the CYBB gene, which encodes the 91-kD glycoprotein gp91, the largest component of the oxidase.The authors recently started the molecular characterization of X-CGD in 18 patients reported to the Argentinean Registry of Primary Immunodeficiency Diseases. The authors reviewed data from clinical records to examine the relationship of clinical presentation and the type of mutations responsible for the genotype.The frequency and type of infections present in these patients were similar to prior reports. However, pulmonary tuberculosis was observed in the group as well as unusual complications such as eosinophilic cystitis, hepatic abscess with cholangitis, and chronic orchitis. Eleven different mutations in the CYBB gene were identified, and seven of them were novel. The types of mutations were intronic, single-nucleotide substitution resulting in nonsense or missense codons and one or two nucleotide deletions resulting in frameshifts. Molecular studies of 18 mothers revealed X-CGD carrier status in all but 2.No correlation existed between the type of mutation and the clinical phenotype of the disease: the molecular defects identified resulted in no expression of the flavocytochrome b558 in patients' neutrophils, leading to the X91°-CGD phenotype. The lack of gp91 protein could explain the early onset and the severity of the clinical manifestations of CGD in this group of patients from Argentina.