Background: Reports about side effects from cromolyn sodium (DSCG) are few and only a minority of them indicate the possibility of an immediate type I hypersensitivity reaction. Methods: We report an 8-year-old boy with a history of seasonal rhinoconjunctivitis and asthma. The patient reported two immediate episodes of acute asthma following inhalation of a cromolyn sodium (DSCG) capsule with an interval of 6 months. The latter occasion was also associated with conjunctivitis and generalized urticaria, requiring emergency treatment. Results: An end-point prick test elicited a 4-mm wheal at 10 mg/mL with DSCG solution for inhalation and DSCG eye drops. An end-point intradermal skin test with DSCG solution for inhalation elicited a 12-mm mean diameter wheal at 10 mg/mL. During the intradermal test, the patient developed conjunctivitis and wheezing with a FEV(1) fall of 27% from baseline. Controlled conjunctival and bronchial challenge tests were positive. The bronchial challenge test was repeated 3 years later showing a FEV(1) fall of 22% five minutes after inhalation of 1 mg/mL DSCG during one minute. A leukocyte histamine release test performed by an autoanalysis fluorometric procedure, with several dilutions of DSCG, was negative. Conclusions: This case of DSCG anaphylaxis satisfies the criteria for an IgE-mediated reaction. We believe that thought should be given more frequently to this mechanism when patients report adverse reactions to DSCG.