Azoles are the primary oral treatment for aspergillosis, but resistance in *Aspergillus fumigatus* has increased. A study of 519 isolates found 5% itraconazole resistance, with 65% cross-resistant to voriconazole and 74% to posaconazole. Most resistant isolates had mutations in the Cyp51A gene, which encodes the target enzyme for azoles. These mutations led to structural changes that reduced drug binding. The study identified 18 amino acid changes in Cyp51A, four of which were novel. Resistance evolved from originally susceptible strains, with different mutations in the same strain and microalterations in microsatellite repeat numbers. Azole resistance is an emerging problem, possibly developing during therapy. Invasive aspergillosis in immunocompromised patients is difficult to diagnose and treat, with high mortality. Chronic and allergic aspergillosis are increasingly recognized, and azoles are the only licensed oral drugs for treatment. Amphotericin B and caspofungin are used for invasive aspergillosis but are less effective for chronic and allergic cases. Itraconazole resistance in *Aspergillus* was first reported in 1997, and since then, only a few cases have been published. The emergence of itraconazole resistance alone is concerning, but widespread cross-resistance would be devastating. The primary resistance mechanism in *A. fumigatus* is mutation in the Cyp51A gene, which encodes the target enzyme for azoles. Mutations in specific codons (54, 220, 98) are associated with resistance. Other mutations have been reported, and additional resistance mechanisms are postulated. The study analyzed 34 itraconazole-resistant isolates and found 18 amino acid changes in Cyp51A, four of which were novel. Microsatellite typing showed resistant mutants evolved from originally susceptible strains, with different Cyp51A mutations in the same strain and microalterations in microsatellite repeat numbers. The study also found that resistance evolved independently in different patients. The study found that 5% of 400 isolates were resistant to itraconazole, with a 7% frequency in the full collection. Resistance increased significantly since 2004. Of the 17 patients studied, 13 had prior azole exposure, and 8 infections failed therapy. The study identified multiple mutations in Cyp51A, including L98H, H147Y, G448S, and P216L. Some isolates showed pan-azole resistance. The study also found that resistance evolved in the lung, not from environmental sources. The high frequency of resistance in the study may be due to the specializedAzoles are the primary oral treatment for aspergillosis, but resistance in *Aspergillus fumigatus* has increased. A study of 519 isolates found 5% itraconazole resistance, with 65% cross-resistant to voriconazole and 74% to posaconazole. Most resistant isolates had mutations in the Cyp51A gene, which encodes the target enzyme for azoles. These mutations led to structural changes that reduced drug binding. The study identified 18 amino acid changes in Cyp51A, four of which were novel. Resistance evolved from originally susceptible strains, with different mutations in the same strain and microalterations in microsatellite repeat numbers. Azole resistance is an emerging problem, possibly developing during therapy. Invasive aspergillosis in immunocompromised patients is difficult to diagnose and treat, with high mortality. Chronic and allergic aspergillosis are increasingly recognized, and azoles are the only licensed oral drugs for treatment. Amphotericin B and caspofungin are used for invasive aspergillosis but are less effective for chronic and allergic cases. Itraconazole resistance in *Aspergillus* was first reported in 1997, and since then, only a few cases have been published. The emergence of itraconazole resistance alone is concerning, but widespread cross-resistance would be devastating. The primary resistance mechanism in *A. fumigatus* is mutation in the Cyp51A gene, which encodes the target enzyme for azoles. Mutations in specific codons (54, 220, 98) are associated with resistance. Other mutations have been reported, and additional resistance mechanisms are postulated. The study analyzed 34 itraconazole-resistant isolates and found 18 amino acid changes in Cyp51A, four of which were novel. Microsatellite typing showed resistant mutants evolved from originally susceptible strains, with different Cyp51A mutations in the same strain and microalterations in microsatellite repeat numbers. The study also found that resistance evolved independently in different patients. The study found that 5% of 400 isolates were resistant to itraconazole, with a 7% frequency in the full collection. Resistance increased significantly since 2004. Of the 17 patients studied, 13 had prior azole exposure, and 8 infections failed therapy. The study identified multiple mutations in Cyp51A, including L98H, H147Y, G448S, and P216L. Some isolates showed pan-azole resistance. The study also found that resistance evolved in the lung, not from environmental sources. The high frequency of resistance in the study may be due to the specialized