Duplicate patient records can increase cost and medical errors. We assessed the association between demographic factors, comorbidities, healthcare usage and duplicate electronic health records. We analyzed the association between duplicate patient records and multiple demographic variables (race, Hispanic ethnicity, sex and age) as well as Charlson comorbidity index (CCI), number of diagnoses, and number of healthcare encounters. The study population included 3,018,413 patients seen at a large urban academic medical center with at least one recorded diagnosis. Duplication of patient medical records was determined by using a previously validated enterprise Master Person Index. Unknown or missing demographic data, Black race when compared to White Race (OR 1.35, p < 0.001), Hispanic compared to non-Hispanic ethnicity (OR 1.48, p < 0.001), older age (OR 1.01, p < 0.001), and "Other" sex compared to female sex (OR 4.71, p < 0.001) were associated with higher odds of having a duplicate record. Comorbidities (CCI, OR 1.10, p < 0.001) and more encounters with the health care system (OR 1.01, p < 0.001) were also associated with higher odds of having a duplicate record. In contrast, male sex compared to female sex was associated with lower odds of having a duplicate record (OR 0.88, p < 0.001). The odds of duplications in medical records were higher in Black, Hispanic, older, non-male patients with more healthcare encounters, more comorbidities, and unknown demographic data. Understanding the epidemiology of duplicate records can help guide prevention and mitigation efforts for high-risk populations. Duplicate records can contribute to disparities in health care outcomes in minority populations.