This study validated a hybrid mercury-free device as a replacement of the mercury sphygmomanometer for professional use, and also as a standard for future validations. A validation study was performed according to the European Society of Hypertension International Protocol 2010 (ESH-IP) in 33 subjects using simultaneous blood pressure (BP) measurements. A total of six BP measurements were taken per participant simultaneously by a supervisor (S; hybrid auscultatory device Nissei DM3000) and two observers (A and B; mercury sphygmomanometers). ESH-IP analysis (99 BP readings): mean device-observer systolic/diastolic BP difference 0.2±2.0/0.1±2.0 mm Hg; systolic BP differences ≤5/10/15 mm Hg in 97/99/99 readings, respectively (diastolic 98/99/99). All 33 subjects had 2 of 3 BP differences ≤5 mm Hg and none without a difference ≤5 mm Hg. Further analysis (198 BP readings): mean differences S-A 0.1±2.4/0.2±2.4 mm Hg (systolic/diastolic), S-B 0.3±2.1/0.2±2.2, A-B 0.2±2.4/0.0±2.3; differences ≤2 mm Hg S-A in 88/84% (systolic/diastolic), S-B 87/85%, A-B 87/86% and ≤4 mm Hg S-A 95/96%, S-B 95/96%, A-B 95/98%. In conclusion, a hybrid mercury-free auscultatory BP monitor comfortably passed the ESH-IP 2010 requirements and has the same level of accuracy as the mercury sphygmomanometer. This device appears to be a reliable alternative to the mercury sphygmomanometer for professional use and also as a standard for future validations.