Sternal osteomyelitis due to Aspergillus fumigatus after cardiac surgery occurred in two nonimmunosuppressed patients. The clinical features of the infection were markedly different in the two cases. In the first patient, sepsis showed a late and insidious onset followed by slow progression. In the second case, fungi were isolated from wound swabs within a few days of surgery and the clinical picture showed acute onset and rapid progression. Only a few cases of sternal osteomyelitis due to Aspergillus have been described previously after cardiac surgery. Aspergillus infection should be considered in the differential diagnosis of mediastinitis after cardiac surgery, especially in a clinical setting of otherwise unexplained sepsis or nonhealing wound despite apparently adequate treatment.