Citrobacter species are motile Gram-negative bacilli that cause disease in humans, such as urinary tract infection, pneumonia, superficial and deep wound infections, gastroenteritis, meningitis, bacteremia, and rarely endocarditis. In those cases of endocarditis, intravenous drug use has been associated with Citrobacter species. Gram-negative organisms are present in less than 10% of cases of endocarditis in intravenous drug users. We present a case of tricuspid valve endocarditis in an intravenous drug user caused by Citrobacter diversus alone.