Small-angle X-ray scattering (SAXS) was performed on single-crystal chemical vapor deposition (CVD) diamonds with low nitrogen concentrations, which were fabricated by microwave plasma-assisted chemical vapor deposition at high growth rates. High optical quality undoped 500 m-thick single-crystal CVD diamonds grown without intentional nitrogen addition proved to be excellent as windows on SAXS cells, yielding parasitic scattering no more intense than a 7.5 m-thick Kapton film. A single-crystal CVD diamond window was successfully used in a high-pressure SAXS cell. © 2012 International Union of Crystallography Printed in Singapore-all rights reserved.