Abstract Doppler broadening of annihilation radiation (DBAR) measurements have been performed in uniaxially hot‐drawn poly(methylmethacrylate) (PMMA) samples. The DBAR spectra were deconvoluted into three Gaussians. The full width at half‐maximum of the narrow component which is due to para‐Positronium (p‐Ps) self‐annihilation is under discussion. An anisotropy of the free volume holes (FVHs) has been detected by measuring the deformed samples at the stretching and transverse directions. The sample deformed at 280% was also measured as a function of the orientation angle (0°–90°) with respect to the stretching direction. The momentum distribution of p‐Ps, which is considered as a structureless particle confined in FVH of ellipsoidal or cuboid shape, was calculated as a function of the potential well size and depth and compared with experiment. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)