OBJECTIVE To carry out a data quality audit for the consistency and quality of immunization monitoring in Kasserine governorate in Tunisia- where immunization coverage rates more than 100%- negative dropout and conflicting coverage rates had been reported. METHODS In a randomly selected sample of 12 primary health care facilities in 2 districts all files used to record immunization data were checked to verify the accuracy of the reported 3rd dose of diphtheria-tetanus-pertussis vaccine during a calendar year. RESULTS The results found frequent over-reporting or under-reporting of doses being administrated in all health facilities. The regional verification factor was estimated as 85% and quality index was 55%. CONCLUSIONS Data quality audit provides a effective tool for self-assessment implementation and developing a critical analysis of the quality of routine immunization data at all levels of health service.