Temperament traits and anxiety have been linked to varying degrees of neurotransmitter imbalances in neurophysiological systems of regulating behaviour. The diversity of neurotransmitters implicated in anxiety symptoms raises questions as to whether the multiple neurotransmitter systems secondarily express dysfunction in a higher-level system, which modulates their activity. This study analyzed the predictions of the neurochemical functional ensemble of temperament (FET) model that proposes that a dysregulation of the opioid receptors acting on monoaminergic and GABA systems gives rise to the symptoms of GAD. The study investigated the coupling of sex, age and temperament traits with generalized anxiety disorder (GAD) across three age groups (17–24, 25–45, 46–65 years). The records of patients aged 65–85 years old were also examined but showed significantly less presence of GAD in comparison to other age groups. Temperament was assessed using the activity specific 12-trait structure of temperament questionnaire. Consistent with the hypotheses of the FET, patients with GAD reported lower mean scores on the traits of social-verbal endurance, mental endurance, plasticity and sensation seeking and higher mean scores in the trait of impulsivity, than healthy individuals. GAD was associated with significantly lower self-confidence in women than in men. The results suggest that new versions of the DSM should consider an increase of impulsivity and a decrease in plasticity of behavior as criteria symptoms of anxiety. Moreover, the results suggest that the current criterion of fatigue should be specified as more related to social-verbal and mental aspects and less to physical aspects of endurance.