The defects and properties of a precipitation hardening Al-Cu alloy 2017 were studied after rolling at room temperature (RT) and cryogenic (liquid N-2) temperature (CT). It is found that CT rolling produced practically the same hardness as RT rolling for a wide range of rolling strains. However, electrical resistivity measurement revealed a clear difference indicating different defect structures in the CT- and RT-rolled samples. This difference led to higher hardness, after subsequent ageing, for samples processed by CT rolling. It is deduced that precipitation occurred during RT rolling, which compensated for the effect of lower dislocation density (evaluated from X-ray diffraction) in RT-rolled sample, and consequently resulted in similar hardness in both RT- and CT-rolled samples. It is noted that after ageing, CT-rolled sample has higher strength (similar to 35%) than the standard T4 treatment.