BACKGROUND In situ simulation (ISS) enables multiprofessional healthcare teams to train for real emergencies in their own working environment and identify latent patient safety threats. This study aimed to determine ISS impact on teamwork, technical skill performance, healthcare staff perception and latent error identification during simulated medical emergencies. METHODS Unannounced ISS sessions (n=14, n=75 staff members) using a high-fidelity mannequin were conducted in medical, paediatric and rehabilitation wards at Stepping Hill Hospital (Stockport National Health Service Foundation Trust, UK). Each session encompassed a 15 min simulation followed by a 15 min faculty-led debrief. RESULTS The clinical team score revealed low overall teamwork performances during simulated medical emergencies (mean±SEM: 4.3±0.5). Linear regression analysis revealed that overall communication (r=0.9, p<0.001), decision-making (r=0.77, p<0.001) and overall situational awareness (r=0.73, p=0.003) were the strongest statistically significant predictors of overall teamwork performance. Neither the number of attending healthcare professionals, their professional background, age, gender, degree of clinical experience, level of resuscitation training or previous simulation experience statistically significantly impacted on overall teamwork performance. ISS positively impacted on healthcare staff confidence and clinical training. Identified safety threats included unknown location of intraosseous kits, poor/absent airway management, incomplete A-E assessments, inability to activate the major haemorrhage protocol, unknown location/dose of epinephrine for anaphylaxis management, delayed administration of epinephrine and delayed/absence of attachment of pads to the defibrillator as well as absence of accessing ALS algorithms, poor chest compressions and passive behaviour during simulated cardiac arrests. CONCLUSIONS Poor demonstration of technical/non-technical skills mandate regular ISS interventions for healthcare professionals of all levels. ISS positively impacts on staff confidence and training and drives identification of latent errors enabling improvements in workplace systems and resources.