AbstractObjectivesWe describe the harmonized MRI acquisition and quality assessment of an ongoing global OCD study, with the aim to translate representative, well‐powered neuroimaging findings in neuropsychiatric research to worldwide populations.MethodsWe report on T1‐weighted structural MRI, resting‐state functional MRI, and multi‐shell diffusion‐weighted imaging of 140 healthy participants (28 per site), two traveling controls, and regular phantom scans.ResultsHuman image quality measures (IQMs) and outcome measures showed smaller within‐site variation than between‐site variation. Outcome measures were less variable than IQMs, especially for the traveling controls. Phantom IQMs were stable regarding geometry, SNR, and mean diffusivity, while fMRI fluctuation was more variable between sites.ConclusionsVariation in IQMs persists, even for an a priori harmonized data acquisition protocol, but after pre‐processing they have less of an impact on the outcome measures. Continuous monitoring IQMs per site is valuable to detect potential artifacts and outliers. The inclusion of both cases and healthy participants at each site remains mandatory.