Objective measurements of duration of attacks have been performed in 8 (5 female and 3 male) patients suffering from primary first division (V-1) trigeminal neuralgia. The mean age of the patients was 67.5 +/- 11.4 years, and the mean age at onset 64.0 +/- 9.7 years. During the study the patients were off treatment. A total of 192 attacks were witnessed by the authors and exactly timed by a stop-watch. The duration of attacks ranged from 2 to 32 s, with a mean of 6.5 +/- 6.1 s. The unweighted mean was 8.8 +/- 5.7 s, with a range of 2.4-17.5 s. With the present data the duration of attacks of V-1 neuralgia has been exactly determined, and the clinical distinction of V-1 neuralgia from other shortlasting headaches, particularly from SUNCT, has been substantially clarified.