Anidulafungin is a semi-synthetic echinocandin antifungal agent indicated for treatment of candidemia and invasive candidiasis. In vitro and clinical data indicate activity of anidulafungin toward invasive mould infections, however, clinical data in human subjects is limited. A paucity of data exists regarding breakthrough mould infections in immunocompromised patients receiving anidulafungin. We report on two immunocompromised adult patients undergoing therapy for hematologic malignancies who developed probable breakthrough mould infections while receiving anidulafungin.