We investigated the mode of inheritance of chronic tension-type headache in 122 families. The probands were from the Copenhagen Headache Clinic, Denmark. The criteria of the International Headache Society were used. The patterns of segregation of chronic tension-type headache were assessed by complex segregation analysis performed with the computer program POINTER. Of the 122 probands with chronic tension-type headache, 56 had 71 first-degree relatives with chronic tension-type headache. The complex segregation analysis indicates that chronic tension-type headache has multifactorial inheritance.