The present study explores the relationships among a number of personality measures (the Sensation-Seeking Scale, SSS; the State-Trait Anxiety Inventory, and the Susceptibility to Punishment Scale) and some parameters of the pituitary-thyroid axis. The study was carried out on a group of 37 physically and mentally fit female volunteers, none of whom had a personal history of psychiatric or endocrinologic illness. The subjects were controlled for the menstrual cycle. The most relevant result was a significant negative relationship between the SSS score and plasma basal levels of thyroxine (T4) and thyroid-stimulating hormone (TSH). Interaction between T4 and TSH levels with trait anxiety was also observed.