A case of unexpected death due to right-sided infective endocarditis (IE) in a 44-year-old female methamphethamine abuser is presented. The woman was taken to a hospital by ambulance with a high fever having almost lost consciousness. She died about 6 h after admission. Autopsy revealed IE of the tricuspid valve. Septic thrombi from the lung were seen in other organs, and accordingly she was considered to have already been in a septic state on admission. Right-sided IE is relatively rare among the overall cases of IE, and is considered to result in good prognosis. It is also considered that right-sided IE occurs commonly among addictive drug abusers. We should therefore bear in mind that the presence of right-sided IE may be a predicting factor of drug abuse even if the injection site is not clearly visible, and for this reason, a toxicological analysis of the addictive drugs should be carried out.