Abstract Defects in potato tubers that are brought about by unfavourable environmental factors that alter normal plant and tuber growth are called physiological disorders. The major causes of physiological disorders include improper cultural, storage or handling practices, high or low temperatures, and inadequate, excessive or uneven soil moisture or nutrient levels. Often, a disorder is caused by the combined effects of environment and cultural practices. Physiological disorders affect the external and internal appearance of tubers. Losses from many physiological disorders can be minimized by using good cultural practices that promote uniform plant and tuber growth over the course of the growing season, and by maintaining proper storage conditions. This chapter describes some tuber physiological disorders, including cracking, enlarged lenticels, greening, elephant hide, second growth, skinning and scald, pink eye, brown centre and hollow heart, bruise, blackheart, translucent end/jelly end, internal brown spot and heat necrosis, vascular discoloration, and internal anthocyanin discoloration.