OBJECTIVE: To determine the differences in the quality of treatment for presumptive malaria received by different socio-economic status (SES) groups in Nigeria. METHODS: The study was conducted in southeast Nigeria. A household survey was used to collect data on patterns of use of different providers for treatment of adult and childhood malaria. The quality of services provided by different provider types was assessed using treatment vignettes. Quality scores for the different providers were computed based on their responses to the different points raised in the vignettes. Patterns of household treatment seeking for fever were disaggregated by SES, and then weighted by quality score to indicate the overall quality-weighted utilization by SES and the average quality of a visit by a member of each SES group. Equity ratios (poorest/least poor) provided the measure of inequity in quality-weighted utilization of different providers. RESULTS: In treatment of adult malaria, higher SES groups used more of public and private hospitals, while lower SES groups used more of traditional healers. In case of children, higher SES used more of healthcare centres and private hospitals and lower SES groups used more of pharmacy shops. The lowest quality of services was measured among laboratories, patent medicine dealers (PMDs), mixed goods shops and pharmacies, all of which are private. The highest scores were observed among the two types of public providers (public hospital and healthcare centres). The quality of treatment services utilised by consumers decreased as SES decreased. However, when the quantity normalized index was used this SES disparity almost disappeared. The resulting equity ratio was 0.96 for adults and 0.94 for children. CONCLUSION: Everybody used poor quality malaria treatment services but the poor people used providers with poor quality malaria treatment services more than others. The major driver of disparities in use of different providers by different SES was the greater number of visits of the higher SES groups, rather than the higher quality of the providers they used. Interventions should be developed to improve quality of treatment seeking behaviour and provision practices.