Changes in shape of internally pressurized tubes caused by operating temperatures and pressures are enhanced by fast neutron irradiation. Lengths and diameters of Zr-2.5 wt% Nb pressure tubes in CANada Deuterium Uranium-Pressurized Heavy Water (CANDU-PHW) power reactors and test reactors have been monitored periodically over the past 15 years. Axial and transverse strain rates have been evaluated in terms of the operating variables and the crystallographic texture and anisotropic microstructure of the extruded and cold-drawn tubes. The anisotropic deformation can be described by models for creep and irradiation growth in which the anisotropy factors are calculated from texture. It is assumed that prismatic slip is the dominant creep mode and that growth occurs by net fluxes of interstitials to a nonrandom distribution of 〈a〉 type edge dislocations and vacancies to 〈a〉 type screw dislocations, 〈c〉 type edge dislocations, and grain boundaries. The equations based on data from the Pickering Generating Station and WR1 test reactors give good agreement with measurements on internally pressurized tubes in Bruce Generating Station and the National Reactor Universal (NRU) test reactor and uniaxially stressed specimen in NRU.