In a questionnaire survey we determined the prevalence of visual symptoms and eye strain factors in a group of chronic headache sufferers as compared with age- and sex-matched controls. The visual symptoms studied were those not specific for headache, i.e., sensitivity to light and blurred vision. Sensitivity to light in the absence of headache was reported by 27.8% of controls and 44.7% of headache sufferers (p less than 0.05). The latter figure increased to 71.3% when headache was actually present (p less than 0.001). Blurred vision occurred in 13.5% of controls and 7.4% of headache sufferers (not significant). In the presence of headache, the latter figure increased to 44.7% (p less than 0.01). Of the eye strain factors studied, bright light was reported to precipitate headache in 29.3% and to aggravate it in 73.4%. For reading, these figures were 16.0% and 55.3%, respectively; for working at the computer screen, 14.5% and 31.3%; and for watching television, 6.4% and 27.7%. We conclude that visual symptoms are more common in chronic headache and eye strain factors more important than is generally recognized.