Repetitive low-frequency electrical stimulation (LFS) induces pain inhibition in healthy volunteers and in animals, but it is unknown whether it has an analgesic effect in patients with headache. The aim of this study was to investigate if LFS could induce prolonged pain inhibition, called long-term depression (LTD), in patients with chronic tension-type headache (CTTH). Twenty CTTH patients and 20 healthy volunteers were exposed to 20 min LFS (1 Hz) to the forehead. LTD was measured as a decrease in pain response to electrical stimulation in a 1-h post-LFS period following LFS. The LFS induced a significant and stable inhibition of pain (LTD) both in patients with CTTH (post-LFS average decrease in pain rating: 19.6 {+/-} 3.9%, all P < 0.005, Holm-Sidak) and in healthy controls (30.1 {+/-} 5.0%, all P < 0.001, Holm-Sidak). During the LFS period, the pain ratings decreased consistently in both groups. In conclusion, a significant and stable pain inhibition (LTD) can be induced in CTTH patients by LFS