We describe herein 98 hematopoietic stem cell transplant (HSCT) recipients with invasive aspergillosis (IA) (refractory in 83) who received micafungin either alone (8 patients) or in combination with other licensed antifungal therapies (OLAT) (90 patients). Of the 8 monotherapy patients, 4 were failing OLAT, received de novo micafungin, or were intolerant to prior OLAT (2 patients each). Of the 90 patients treated with combination, 7 had de novo IA and 83 had refractory infection. Most patients (81) had pulmonary IA, 42 (43%) had graft-versus-host disease (GVHD), and 26 (27%) were neutropenic (absolute neutrophil count <500 cells/mm(3)) at onset of treatment. Successful response was seen in 25/98 (26%); an additional 12 patients achieved stable disease. Response was seen in 2/9 (22%) in de novo treatment, 21/87 (24%) in refractory patients, and 2/2 (100%) in toxicity failure patients. Additionally, response was seen in 22 of the 90 (24%) patients treated with combination therapy, and in 3 of 8 (38%) patients who were treated with micafungin alone. No significant differences in responses were found based on type of HSCT, GVHD status, site of IA, or Aspergillus species, and no significant toxicity was seen. Micafungin was well tolerated, even at high doses, and is a reasonable option for treatment of IA in this high-risk patient population.