•Fast, cheap and reliable method for quantitation of GHB-GLUC in whole blood.•LOD and LLOQ of 0.2mg/L.•First GC–MS/MS method for GHB-GLUC.•First application to post-mortem whole blood samples. γ-Hydroxybutyric acid (GHB) is an endogenous compound with a historical use, both in licit and illicit terms. Importantly, the post-mortem behavior of GHB has been studied due to the possibility of using this compound as a biomarker for estimating the post-mortem interval (PMI). However, the post-mortem behavior of the recently discovered glucuronated GHB metabolite (GHB-GLUC) has not been studied. Nevertheless, GHB-GLUC may also have potential both to assist in PMI determination and also to increase the window of detection of GHB consumption. In this work, for the first time, a reliable method using GC–MS/MS for the quantification of GHB-GLUC in whole blood samples was developed and validated, with a simple, fast and cheap sample pretreatment. The method proved to be specific, precise, linear in a work range between 200 and 5000ng/mL, with LOD and LOQ of 52.65ng/mL and 200ng/mL, respectively, and an extraction recovery of 51%. Furthermore, the method was applied to a set of real post-mortem blood samples non-related with GHB intoxication and the obtained results were also discussed.