Caspofungin, an antifungal agent that acts on the cell wall by inhibiting β-1,3-glucan synthesis, is likely to be effective for treating Pneumocystis pneumonia, because one of the identifying characteristics of Pneumocystis jirovecii is the presence of β-1,3-glucan in its cell wall. Previous case reports in which the efficacy of caspofungin was found to be favourable have supported this hypothesis. However, of 4 HIV-negative patients who received caspofungin as a salvage regimen at Asan Medical Center, none showed a response. Our negative experience opposes the optimistic view of caspofungin use for Pneumocystis pneumonia expressed in previous reports.