The defect structures in single crystals of thiourea, (NH 2) 2CS (space group Pnma), grown by evaporation from a solution in water and methanol are examined by X-ray topography. The crystals exhibit the growth faces {100}, {010} and {101} growth sectors they are rather perfect: large parts of these regions are free from dislocations and inclusions. The {010} growth sectors are considerably disturbed by growth layers consisting of microscopically small inclusions with solution, which cause the milky appearance of these sectors. The crystals contain numerous rectilinear dislocation lines radiating from the seed crystal and from inclusions. Many of them have predominant screw components and Burgers vectors parallel to [100], [010], [001] and [101]. Moreover, in {100} and {001} growth sectors, there are pure edge dislocations running essentially parallel to the growth direction. The topographs show forests of hairpin-like dislocation half-loops extending from the {101} surfaces into the crystal, with glide direction [001] and glide plane (100). They have been introduced by plastic deformation as the consequence of stress which has unintentionally been applied while handling the crystals. The half loops reveal the anisotropic plasticity of thiourea. The glide direction is parallel to the direction of the shortest lattice translation, the glide plane coincides with the plane of cleavage of the crystal.