Background: Diabetes mellitus may be a risk factor to Pseudomonas aeruginosa infection. Diabetes mellitus is a metabolic syndrome which causes a dysfunction of the hosts immune system. Pseudomonas aeruginosa is an opportunistic pathogen. Objective: To determine the correlation between diabetes mellitus and Pseudomonas aeruginosa infection Methods: The study is conducted in the internal medicine ward of RSUD Dr. Soetomo, a tertiary hospital in Indonesia in 2021. The population of this study is all patients aged 18 or above with positive blood, sputum, urine, and pus cultures.This study uses systematic random sampling for non-Pseudomonas aeruginosa infection patients and total sampling for Pseudomonas aeruginosa infection patients. Data was obtained through logbooks of the microbiology department and the patients medical records. Only the first culture of each type per patient was considered. Analysis was done using the relative risk (RR) formula. Result: The relative risk of diabetes mellitus in Pseudomonas aeruginosa infections is 1.75 for bloodstream infection, 0.88 for pneumonia, 1.68 for urinary tract infection, and 0.87 for pyogenic infection. Conclusion: When compared to non-Pseudomonas aeruginosa infections, diabetes mellitus is a risk factor for bloodstream and urinary tract infections and a protective factor for pneumonia and pyogenic infections.