AbstractPurpose:To present the use of a quality control ice‐water phantom for diffusion‐weighted magnetic resonance imaging (DW‐MRI). DW‐MRI has emerged as an important cancer imaging biomarker candidate for diagnosis and early treatment response assessment. Validating imaging biomarkers through multicenter trials requires calibration and performance testing across sites.Materials and Methods:The phantom consisted of a center tube filled with distilled water surrounded by ice water. Following preparation of the phantom, ≈30 minutes was allowed to reach thermal equilibrium. DW‐MRI data were collected at seven institutions, 20 MRI scanners from three vendors, and two field strengths (1.5 and 3T). The phantom was also scanned on a single system on 16 different days over a 25‐day period. All data were transferred to a central processing site at the University of Michigan for analysis.Results:Results revealed that the variation of measured apparent diffusion coefficient (ADC) values between all systems tested was ±5%, indicating excellent agreement between systems. Reproducibility of a single system over a 25‐day period was also found to be within ±5% ADC values. Overall, the use of an ice‐water phantom for assessment of ADC was found to be a reasonable candidate for use in multicenter trials.Conclusion:The ice‐water phantom described here is a practical and universal approach to validate the accuracy of ADC measurements with ever changing MRI sequence and hardware design and can be readily implemented in multicenter clinical trial designs. J. Magn. Reson. Imaging 2011. © 2011 Wiley‐Liss, Inc.