We studied the interrelation of chronic tension-type headache with and without medication overuse (CTTH) and migraine in a random sample of 30 000 persons aged 30-44 years. They received a mailed questionnaire. Those with a possible chronic headache were interviewed by neurological residents. The International Classification of Headache Disorders was used. A total of 386 persons had CTTH. Compared with the general population, men had a 2.8-fold and women a 2.4-fold significantly increased risk of migraine without aura (MO). The risk of migraine with aura (MA) was not increased. The mean age at onset of CTTH was significantly higher in those with than in those without co-occurrence of MO. Bilateral MO attacks were significantly more frequent in those with age at onset of CTTH prior to age at onset of MO compared with those with age at onset in reverse order. CTTH and MO are interrelated, possibly in a complex matter. In contrast, CTTH and MA are not interrelated.