Introduction: Healthcare-associated transmission of the hepatitis C virus (HCV), although rare, remains one of the described modes of transmission. On May 7, 2015, the Paris-Nord Center for the Coordination of the Fight Against Nosocomial Infections (CClin) received a report of a case of HCV seroconversion, identified in April 2015 in a medical dialysis unit in a patient undergoing dialysis during the same sessions as another patient known to be an HCV carrier. The objective of this study was to identify the factors that contributed to this HCV transmission between two patients in a dialysis center. Materials and Methods: After reconstructing the timeline of events, conducting an audit of practices, and interviewing center staff individually, we used the ALARM method to identify the immediate, contributing, and latent causes underlying this HCV transmission. Results: The National Reference Center (NRC) for Viral Hepatitis confirmed that the two strains were identical. The immediate causes of transmission identified were: suboptimal adherence to standard precautions, lack of risk control regarding blood splashes, and poor hand hygiene among patients. The contributing causes are related to: patients (frequent post-dressing bleeding, not always well-trained in hygiene measures); healthcare professionals (failure to verify patients’ hand hygiene, lack of awareness of the viral risk associated with splashes); the team (significant mutual assistance among professionals leading to disorganization of care with frequent interruptions of tasks); to the work environment. Latent causes include: organizational factors, such as the turnover of one-third of the team starting in June 2014 and the need to train new staff, as well as the absence of a patient education policy. Discussion: This case study allowed us to identify several practice failures that may have contributed to nosocomial HCV transmission in a medical dialysis unit. The ALARM method appears highly relevant for helping to implement measures aimed at improving the organization of care.