Caspofungin acetate is the first member of the novel echinocandin class of antifungal drugs to be marketed in the United States. It has recently been approved for use in patients with invasive aspergillosis who are refractory to or intolerant of conventional therapy. Accordingly, its safety profile is particularly important to review. The safety and tolerability of caspofungin have been examined in 623 persons, including 295 patients who received >/= 50 mg/day for at least one week in clinical studies. In the 263 patients, given caspofungin in randomized double-blind active-control trials to date, there have been no serious clinical or laboratory drug-related adverse events; caspofungin was discontinued in only 2% of these patients because of drug-related adverse experiences. Caspofungin may have potentially important drug interactions with cyclosporine and tacrolimus.