Hyperhydricity is a morphological and physiological disorder affecting plants regenerated in vitro. This malformation is associated with excessive hydration and abnormal shoot morphogenesis such as glassy water-soaked appearance of shoots. This undesirable phenomenon is a frequent problem in sunflower tissue culture systems and has been described by visual symptoms but there is no information on the anatomic structure of the affected shoots. In this paper we describe anatomic features of normal and hyperhydric sunflower shoots regenerated in vitro. The hyperhydric shoots were classified in four cat egories according to different abnormalities observed at the morphological level. The anatomic structure of leaves and stems of normal shoots did not dif fer from control seedlings. In contrast, hyperhydric shoots presented various anatomic defects, such as reduction of palisade parenchyma, an increase in cellular volume, hypolignification of vascular system and hypertrophy of corti cal and pith parenchyma. In addition, a crescent disorganization at the ana tomic level was observed among the different types of hyperhydric shoots. This study provides a characterization of the anatomic responses induced by hyper hydration in tissue culture regenerated sunflower plants.