Due to suspected background irradiation, the incidence of thyroid nodules and carcinomas is increasing in the human population. If irradiation is the cause then great apes may have a similar frequency of this disease. If the rise is due to specific human factors such as diet then the incidence in gorillas may be low. This study will help to develop a methodology for thyroid ultrasound evaluation in gorillas, will help to establish a database of thyroid health in the population and may provide answers to the health of the human population as well.