This study on primary chronic daily headache was based on the 1996 proposed revision of the diagnostic criteria of the International Headache Society (IHS). To investigate the relative frequency, clinical characteristics, and associated features of primary chronic daily headache in Omani patients, 171 patients visiting the Neurology Clinic at Sultan Qaboos University Hospital were evaluated. Forty-five percent was diagnosed as suffering from primary chronic daily headache (female to male ratio, 1.7:1). Sixty-two percent suffered from transformed migraine and 34% from chronic tension-type headache. The average age across sexes was 32.3 +/- 12.3 years. A dull heavy feeling in the head was reported by 58% of patients and was associated in less than one third with associated features characteristic of migraine. All headache types shared the same trigger factors. All patients were taking medication, predominantly analgesics, at the time of their first visit. We concluded that primary chronic daily headache is very common with the relative frequency of transformed migraine being similar to that found in Mediterranean studies. Also in Oman, chronic use/overuse of analgesics and nonsteroidal anti-inflammatory drugs is a problem that coexists with primary chronic daily headache. Finally, the proposed revised IHS criteria are highly recommended as a standard classification system for this type of headache.