Background: Thromboelastometry is a whole blood assay performed to evaluate the viscoelastic properties during blood clot formation and lysis. Rotation thromboelastography (ROTEM((R)), Pentapharm GmbH, Munich, Germany) has overcome some of the limitations of classic thromboelastography. So far, no clinical validation on reproducibility (inter- and intra-assay variability) and sample stability over time has been published. Methods: To evaluate the pre-analytic aspects, sample stability over time was assessed in 48 patients in eight age groups. Citrated blood was stored at room temperature. Tests measured every 30min from T 0min up to T 120min on two ROTEM((R)) devices were INTEM (ellagic acid activated intrinsic pathway), EXTEM (tissue factor-triggered extrinsic pathway) and FIBTEM (with platelet inhibitor (cytochalasin D) evaluating the contribution of fibrinogen to clot formation). Precision by intra- and inter-assay variability was evaluated at two points of time in 10 volunteers. Finally, reference intervals and effect of age and sex were evaluated. Results: Blood was stable over 120min and no significant differences in ROTEM((R)) results were found. Maximum clot firmness measurements had a coefficient of variation of <3% for EXTEM, <5% for INTEM and <6% for FIBTEM. For clot formation time, the coefficient of variation was <4% for EXTEM and <3% for INTEM. Coefficient of variation for angle alpha was <3% for EXTEM and <6% for INTEM. The coefficient of variation for clotting time was <15% for both EXTEM and INTEM. Small but significant differences between ROTEM((R)) devices were found for maximum clot firmness in FIBTEM and INTEM as well as clot formation time and alpha angle in INTEM. Conclusions: ROTEM((R)) yields stable results over 120min with a minimal variability on the same ROTEM((R)) device. However, small but significant differences between ROTEM((R)) devices were observed. Analysis should be performed on the same ROTEM((R)) device if small differences are of importance for treatment.