Caspofungin, an echinocandin antifungal agent, is active against invasive Aspergillus and Candida infections. In a phase I study in healthy volunteers, mild transient increases in serum aminotransferases were observed with the concomitant administration of caspofungin and cyclosporin A (CsA). As a result, it is recommended that the concomitant use of the two drugs be limited to those settings with appropriate risk-benefit balance. We retrospectively assessed safety data in 14 patients with refractory invasive mycoses who were treated concomitantly with CsA and caspofungin before the drug was licensed in Spain. In all, 13 patients were adults (median age, 31.5 years; range, 14-67 years). The average duration of concomitant therapy was 15 days (range, 2-43 days). No clinically significant elevations of serum aminotransferases were observed, and no patient had concomitant therapy discontinued or interrupted due to a drug-related adverse event. In this study of a limited number of patients, the coadministration of caspofungin and CsA was generally well tolerated.