BACKGROUND The quality of external chest compressions (ECC) is influenced by the surface supporting the patient. The aim of this study was to compare chest compression depth with and without a rigid backboard. The authors hypothesized that the presence of a backboard would result in an increased depth of chest compressions. METHODS A randomized, double-blinded, cross-over trial. We simulated in-hospital cardiac arrest using a resuscitation manikin placed in a standard hospital bed. In total, 23 hospital orderlies were randomly assigned to perform ECC for 2 min on two identical ResusciAnne manikins, under one of which a rigid backboard had been placed. Data were recorded using the Laerdal PC-Skill Reporting System. RESULTS Mean chest compression depth increased from 43 to 48 mm (P < 0.0001) when a backboard was present (mean difference 5 mm, 95% CI 3.6-7.5 mm, SD 4.6). There was a significant increase in mean proportion of compressions >40 mm when using a backboard Mean 92% vs. 69%, P= 0.0007). No difference was found between the two groups in the following variables: duty cycle, compression rate, mean proportion of compressions of correct depth (40-50 mm) or proportion of compressions with incomplete release. CONCLUSIONS Applying a backboard significantly increases depth of chest compressions during cardiopulmonary resuscitation when performed on a manikin model.