Cretinism is a disease marked by arrested physical and mental development and thyroid dysfunction, caused by a deficiency of iodine. It may (more rarely) occur as hypothyroidism, often associated with dwarfism in an individual, in areas with high intake of cassava (myxedematous or classical cretinism). The nervous or neurological type of cretinism more commonly occurs, which is caused by nutritional deficiency of iodine as a foetus and/or during early childhood, and is preventable by dietary iodine supplements. Unlike hypothroidism, the neurological form of cretinism cannot be reversed by the administration of thyroid hormones.
Cretins have physical deformities as well as impaired metabolism and low body temperature. Poor hearing is marked and permanent (often manifest as deaf mutism), and mental retardation is often at the level of idiocy. Cretins are slow moving, sleepy, and halting of speech; the acquisition of knowledge and skills is a difficult and time-consuming process. The height of cretins is well below average (146.7 cm for males and 140 cm for females).