In order to investigate the character of dislocation structures, icosahedral Al-Pd-Mn single quasicrystals were plastically deformed between 821 and 580 ^°C, where quasi-steady state deformation is possible, and down to 482 ^°C in a state of strong work-hardening during loading up to stresses up to about 1.6 GPa. The dislocation structures are imaged in a 1000 kV high voltage transmission electron microscope. At high temperatures, the dislocations are arranged in a three-dimensional network of low dislocation density. At low temperatures, the dislocations form narrow bands of a high dislocation density. Part of the dislocations strongly bow out between obstacles, dislocation debris or jogs, but other dislocations consist of segments oriented crystallographically, connected by smoothly bent segments. In other samples, dislocation loops are arranged close to many different planes but parts of them bow out onto inclined faces. These observations are discussed in the light of existing models of the dynamics of dislocation motion and of the evolution of the dislocation density considering dislocation multiplication and recovery. However, many features observed cannot be interpreted on the basis of the present understanding of the dislocation behavior.