The aim of the present study was to compare the effect of transcutaneous electric nerve stimulation (TENS) with the flat occlusal splint in the treatment of temporomandibular joint (TMJ) disk displacement without reduction. Thirty-one patients were included and randomly selected to be treated 6 weeks with either TENS (90 Hz, 30 min, three times/day) or with a flat occlusal splint (24 h/day. Those selected for the TENS group had one electrode placed over the painful TMJ and another electrode over the anterior temporal muscle. The splint group used a conventional flat occlusal splint with cuspid guidance. Both treatment groups visited the clinic once a week. Symptoms and signs were registered before and after treatment. The intensity of pain was recorded with a visual analogue scale (VAS) and with an electronic pocket-sized recorder (Pain-Track) carried 1 week before and also the last week of treatment for continuous registration of pain. Measured with the VAS, half of the patients treated with splints became pain-free or their TMJ pain improved at least 50% both at rest and with jaw function compared with only 6% in the TENS-treated group. With regard to strictly chewing pain, the VAS-registered pain improved in two-thirds of the splint group, compared with 50% of the TENS group. With the Pain-Track device it was found that in most individuals pain was aggravated at mealtimes. The conclusion was that flat occlusal splints in several respects are better than TENS in the treatment of symptoms associated with TMJ disk displacement without reduction.