In order to evaluate photophobia and phonophobia in cluster headache (CH), light and sound-induced discomfort and pain thresholds were measured quantitatively in 50 patients and 50 sex-matched and age-matched headache-free controls. During bout (i.e., during the active period with attacks), CH patients were more sensitive to light and sound than controls (p < 0.001). Outside bout they did not differ significantly from controls except for binaural stimulation. Patients were more photophobic and phonophobic during bout than in the remission period (p < or = 0.05). However, for those tested during bout, the sensitivity to light and sound was not related to the presence of pain during test, usual pain intensity, or pain laterality. In response to a questionnaire about their sensitivity, a significantly higher proportion of patients considered themselves sensitive during bout than outside (91% vs 46% for light [chi 2 = 5.9, p < 0.05] and 89% vs 49% for sound [chi 2 = 4.7, p < 0.05]). These results indicate that photophobia and phonophobia are important accompanying phenomena of cluster bouts.