Background: The Singapore GSDCS score was developed to enable clinicians predict the risk of nosocomial multidrug-resistant Gram-negative bacilli (RGNB) infection in critically ill patients. We aimed to validate this score in a UK setting. Method: A retrospective case–control study was conducted including patients who stayed for more than 24 h in intensive care units (ICUs) across two tertiary National Health Service hospitals in London, UK (April 2011–April 2016). Cases with RGNB and controls with sensitive Gram-negative bacilli (SGNB) infection were identified. Results: The derived GSDCS score was calculated from when there was a step change in antimicrobial therapy in response to clinical suspicion of infection as follows: prior Gram-negative organism, Surgery, Dialysis with end-stage renal disease, prior Carbapenem use and intensive care Stay of more than 5 days. A total of 110 patients with RGNB infection (cases) were matched 1:1 to 110 geotemporally chosen patients with SGNB infection (controls). The discriminatory ability of the prediction tool by receiver operating characteristic curve analysis in our validation cohort was 0.75 (95% confidence interval 0.65–0.81), which is comparable with the area under the curve of the derivation cohort (0.77). The GSDCS score differentiated between low- (0–1.3), medium- (1.4–2.3) and high-risk (2.4–4.3) patients for RGNB infection (P