Severe combined immunodeficiency (SCID) is characterised by profound quantitative and/or functional T-cell defects and predisposes infants to life-threatening infections, including sepsis that may progress to organ dysfunction and disseminated intravascular coagulation (DIC) with thrombotic and haemorrhagic complications. However, atypical forms such as Omenn syndrome or leaky SCID may present with immune dysregulation and tissue inflammation, complicating the clinical picture. Starting from a clinical case of sepsis in an infant with SCID, a targeted literature review on emergency management of severely immunocompromised patients was performed to improve recognition and management of the critically ill infant with SCID, underscore the role of lymphopenia as a sentinel marker and propose practical recommendations to optimise outcomes in septic complications such as haemodynamic instability and DIC. Managing critically ill infants with SCID requires a coordinated multidisciplinary team (anaesthetist/intensivist, paediatrician, immunologist, transfusion specialist) able to apply resuscitation bundles while balancing infection risks. Each paediatric emergency unit should adopt a local protocol for urgent vascular access selection consistent with best-practice guidance and available resources