Previous studies in headache patients measured the cerebrovascular reactivity (CVR) in response to photic stimulation but they have yielded contradictory results. The purpose of study was to measure CVR of both migraine and chronic tension headache (TTH) patients in response to photic stimulation. The study included 37 migraineurs and 24 chronic TTH patients compared with 50 age- and sex-matched healthy volunteers. Peak systolic, end diastolic, mean flow velocities and CVR (PSV, EDV, MFV, and CVR) were measured using TCD ultrasonography of the middle, anterior, posterior cerebral and vertebral arteries (MCA, ACA, PCA, and VA) before and after 100 s of 14 Hz photic stimulation. A three-way repeated measures ANOVA interaction with main factors of Vessels (MCA, ACA, PCA, VA), Time (pre-post photic) and Groups (migraine, TTH, and control group) revealed significant 3-way interactions for measures of PSV (P = 0.012) and MFV (P = 0.043). In the migraine patients there was significantly higher PSV, EDV, and MFV in the MCA, ACA, and PCA after photic stimulation compared with baseline. The CVR of the MCA was also significantly higher in migraineurs than controls. In the TTH group, there was significantly higher PSV, EDV, and MFV (P = 0.003, 0.012, 0.002 respectively) in the VA after photic stimulation than at baseline. The CVR was significantly higher in the VA of TTH patients than controls. Compared with controls after photic stimulation, the higher CVR of the MCA in migraineurs and of the VA in TTH patients could be used as diagnostic tool to differentiate between the two types of headaches.