Chronic daily headache (CDH) associated with long-term misuse of headache medication is a common clinical problem which is refractory to most treatments. The present study is a retrospective analysis of the effect of drug withdrawal therapy in patients with CDH and frequent long-term use of headache symptomatic medication. One hundred and one adult patients (74 women and 27 men, aged between 16 and 72 years, mean age 43 years) were evaluated 1-3 months after drug withdrawal therapy had been initiated. The mean headache frequency at baseline was 26.9+/-4.0 days per month. Fifty-seven (56%) patients were significantly improved (defined as at least 50% reduction in number of headache days) after a period of drug withdrawal therapy. Based on the outcome of the drug withdrawal therapy, the patients were divided into three categories: group I, those who had between 0 and 10 headache days per month (n = 41), group II, those who had 11-20 days (n = 37), and group III, those who had 21-30 days (n = 23). The mean headache frequencies in groups I, II and III were 5.6+/-2.8 days, 15.7+/-2.5 days and 28.7+/-2.4 days, respectively. Treatment with amitriptyline was offered to patients in whom no improvement had been achieved. Ten of those 22 patients (36%) experienced a significant (> or = 50%) reduction of headache days. It is concluded that out-patient drug withdrawal therapy is the treatment of choice in patients with CDH and frequent long-term use of headache symptomatic medication, and that about one quarter of these CDH patients do not respond to drug withdrawal therapy only.