Asthma with allergic bronchopulmonary aspergillosis (ABPA), a hypersensitivity disease of the lungs due to an immune response to Aspergillus fumigattus (Af) antigens, is rarely seen in children, other than complicating cystic fibrosis. We present the case of a 14 - year- old female teenager with cystic fibrosis (CF), admitted in our hospital with respiratory failure and persistent cyanosis. Chest X-ray showed perihilar and upper lobes pulmonary infiltrates. Her airway cultures were positive for methicillin resistant staphilococcus aureus (MRSA) and non-mucoid Pseudomonas aeruginosa. She was prescribed intravenous antibiotherapy with ceftazidime and vancomycine (to which MRSA and Pseudomonas aeruginosa were susceptible). Pulmonary function testing (PFT) revealed severe obstructive lung disease. After ten days of intravenous antibiotics and first five days of corticosteroid, the patient's FEV1 was 68% of predicted. Total serum IgE and IgE antibodies to Aspergillus fumigatus were elevated. These results raised the possibility of allergic bronchopulmonary aspergillosis (ABPA). The possibility of ABPA should be considered in all pulmonary exacerbation and in order to determine if ABPA is developing or if an exacerbation is occurring, a serial monitoring of IgE levels should be performed.