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Ralstonia spp. are low-virulent environmental Gram-negative bacteria that can cause serious nosocomial infections in immunocompromised patients. We report the characteristics of a cluster of R. insidiosa bacteremia cases occurring in our oncology day ward in Milan, Italy, between January and March 2022. A case was defined as a cancer patient attending our day ward and whose blood culture (performed because of bacteremia symptoms) led to the isolation of Ralstonia insidiosa. An epidemiological investigation was conducted in order to seek the possible source of infection. Seven adult patients received curative or palliative treatment via infusion through a Port-a-Cath (PAC). All developed symptoms within 24 h of the infusion (three during the infusion itself). Ralstonia insidiosa was isolated in the blood drawn from the PAC in all patients. All of the isolates were susceptible to carbapenems, fluoroquinolones, and piperacillin/tazobactam but resistant to aminoglycosides and cephalosporins. Systemic and/or lock antibiotic therapy led to stable symptom resolution and negative blood cultures in five patients, whereas bacteremia recurred in two patients. An epidemiological investigation suggested that extrinsic contamination of antiseptic solutions was the possible cause of the R. insidiosa infections. Although R. insidiosa is not considered a virulent pathogen, clinicians, microbiologists, and infection control teams should be aware about its potential to cause outbreaks of nosocomial bloodstream infections, especially in immunocompromised patients bearing central venous catheters.