The precipitate structure and matrix deformation were examined in a commercial Cu-11.5 at%-Be-0.23 at%-Co alloy by quantitative X-ray diffraction techniques. A model is proposed that is consistent with early electron microscopy results by Bonfield and Edwards [J. Mater. Sci. 9 (1974) 398] and recent advances by Khachaturyan and Laughlin [Acta Metall. Mater. 38 (1990) 1823]. Agreement was found for a precipitate model consisting of highly deformed versions of the equilibrium gamma-phase. This is in accord with earlier results for gamma" and gamma’ precipitates and is further generalized to include the GP zone for this alloy. Two states of deformation are required, i.e. one relatable to gamma" and the GP zone, with a second relatable to a continuous deformation which describes the rotation of the gamma’ precipitate. The matrix becomes and remains severely deformed prior to and through the hardness maximum. Bragg-like matrix peaks become partitioned into three components : quasilines, static diffuse scattering and a residual Bragg peak. The so-called "arrowhead" scattering should be re-examined as a generalized form of Laue scattering, which includes a difference between the square of the scattering amplitudes for the precipitate and the matrix that it replaces.