A pure silica MCM-41 preparation with high crystalline order perpendicular to the channels has been examined using small-angle neutron scattering and the contrast variation method in both the calcined and template-containing forms. This defines various structural features such as template and water distributions and content, local silica density, and surface properties. Adsorption isotherm data, NMR, previous neutron scattering data, and the SANS data allow a choice between proposed models for the channel structure of MCM-41, in terms of the straightness of the channels and their surface roughness.