The lack of measured surface scatter data at extreme ultraviolet (EUV) wavelengths has been commented upon by a number of authors. The need for such data arises primarily in the area of stray light design and analysis. Most stray light software requires knowledge of the bidirectional reflectance distribution (BRDF) for relevant surfaces. Without this measured data, quantitative assessment of stray light effects is difficult, making the confident prediction of instrument performance almost impossible. The Goddard EUV scatterometer was designed to perform such measurements, and the geometry, important design issues, and performance are discussed. This instrument is capable of plane-of-incidence BRDF measurements at EUV wavelengths between 58.1 nm and 121.6 nm, with a lower measurement limit of approximately 10-5 sr-1, and is able to accommodate angles of incidence between 10 and 75 degrees. The scatterometer can measure scatter to within 1.5 degrees of the specular beam, and the scatter angle can be measured to within 0.1 degree. BRDF data is presented for the commonly used visible-diffuser material white Spectralon SRS-99 at 121.6 nm; and for common baffle surfaces Martin Black, black Spectralon SRS-02, and an evaporated Cu black at wavelengths of 58.4 nm and 121.6 nm and angles of incidence of 15 degrees and 45 degrees. The BRDF distribution of a 3000 line/mm Al diffraction grating is also presented.© (1996) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.