Background: Feel4Diabetes was a large-scale, multicenter lifestyle intervention aiming to prevent type 2 diabetes among families from vulnerable population groups in six European countries (Belgium, Bulgaria, Finland, Greece, Hungary and Spain). The current study aimed to describe the process that was followed to harmonize and standardize the measurement of anthropometric (weight, height and waist circumference) and blood pressure (systolic and diastolic) indices, as well as to assess the intra- and inter- observer reliability of these measurements.Methods: A central training workshop was conducted prior to the baseline measurements of the Feel4Diabetes-intervention. One researcher from each intervention country, as well as 12 adults and 12 children (for the anthropometric measurements) and 21 adults (for the blood pressure measurements) participated in this workshop. Technical Error of Measurement (TEM) and reliability (%R) were calculated to assess the reliability of the indices which were assessed to evaluate the outcome of the Feel4Diabetes-intervention. The Feel4Diabetes-intervention is registered athttps://clinicaltrials.gov/(NCT02393872).Results: Intra-observer reliability was found to be higher than 99.5% for all anthropometric measurements in both children and adults. Inter-observer reliability was found to be higher than 98% regarding the anthropometric measurements, while for blood pressure measurements %R was 76.62 and 91.38% for systolic and diastolic blood pressure measurements, respectively.Conclusion: The central training of the Fee4Diabetes-intervention ensured that the data collected for the outcome evaluation of the Feel4Diabetes-intervention in the six European countries at three different time points (baseline, follow-up 1 and follow-up 2) were valid and comparable.