SUMMARY. Although physiotherapists are frequently involved in the treatment of headache when cervical spine dysfunction is thought to be a cause or contributing factor there does not appear to be a consistent definition of treatment success. This study analysed treatment outcome in a population of 112 headache patients presenting for manipulative physiotherapy. Two months after the initial consultation, statistically significant improvements were observed in mean scores for each of headache frequency (P < 0.001), duration (P < 0.05) and intensity (P < 0.001). When a combination of patient estimate of treatment effect and a headache index incorporating scores for frequency, intensity and duration was used to classify treatment outcome, 51 of the 91 subjects analysed at follow-up were deemed to have had a positive response to treatment. This method of classification of treatment outcome appeared to be sensitive to cases where the patient's headaches were improved by factors other than the physiotherapy treatment. However the classification used was less sensitive when the patient's headaches were aggravated by other factors or where there was not consistent improvement or deterioration in the measures of headache frequency, intensity and duration. Copyright 1997 Harcourt Publishers Ltd.