In two females aged 27 and 32 years old, an aggravation of their panic disorder coincided with the appearance of clinical signs of hyperthyroidism. The clinical diagnosis was confirmed with the finding of raised thyroid hormone levels and undetectable TSH levels. These two cases highlight the importance of routine thyroid function assessment in patients with panic disorder, mainly in those with partial response to medications or when symptoms aggravate, despite an adequate treatment (Rev Méd Chile 2001; 129: 187-90).