Fungi can exacerbate symptoms in patients with asthma. To our knowledge, genetic risk factors for fungal-associated asthma have not been described. We present here the cases of 6 children who carried the diagnosis of severe asthma with fungal sensitization, 3 of whom were treated with and responded clinically to itraconazole therapy. All 6 patients were heterozygous for a 24-base pair duplication in the CHIT1 gene, which has been associated with decreased levels of circulating chitotriosidase and susceptibility to fungal infection.