Tension-type headache (TTH) is the most common form of headache in the general population. Diagnosis of TTH is based merely on clinical features and on careful exclusion of all possible causes of headache. Most of the headaches that present in the context of medical disorders (e.g., hypothyroidism, sleep disorders, and hypertensive crisis) have clinical features overlapping with those of TTH; medical history and specific features of the systemic disorder are usually the clues to establish a correct diagnosis. Some medical disorders may worsen a preexisting TTH, and is also possible the comorbidity of TTH with psychiatric disorders and fibromyalgia.