This study was aimed at exploring the completion of death reports, causes of death and the provision of causes of death of patients in the HIV/AIDS surveillance System in Mukdahan province from 1987 to 2005. Quantitative research methodology was employed by four steps. Firstly, the researcher checked patient data against report cards. Next, names, surnames and citizen identification numbers were searched. The researcher then checked causes of death with death data from at least three sources and finally explored the completion of death reports and causes of death. The researcher used descriptive statistics to analyze quantitative data. Qualitative methodology was also applied through informal and in-depth interviews with concerned people including doctors, registrars and death reporters. Data from the interviews was analyzed by the content analysis method. There were 1,267 patients involved in this study. Of these, the deaths of only 239 patients had been reported (18.8 percent). The researcher investigated death data from other sources and found 815 patients (64.3 percent) while 588 were dead (72.1 percent). Only 40.6 percent of death reports had been completed. AIDS was given as the causes of death on the certificate in only 24.1 percent of case. Unknown causes, tuberculosis, lung abnormalities, cancers and tumours in that order were identified as the next biggest causes of death. Mistakes in identifying the cause of death could have been due to several factors. Doctors may have perceived a particular diseases as the cause of death rather than identifying the underlying diseases which was the real cause of death. Village leaders lacked knowledge and guidelines to investigate causes of death. Therefore, their views on the cause were mainly base on the dead’s relatives. Additionally, the underlying cause of death was concealed by the dead’s relatives for fear of rejection by the community and its impacts on their families. The study recommends that the completion of death reports by hospital staff should be over 80 percent parallel to the Bureau of Epidemiology’s criteria. It is also recommended that cross-check of death data between provincial registration offices and Ministry of Interior using citizen ID numbers be done. However, provincial officers should be entitled to access such information. Lastly, wide distribution of information on the underlying cause of death to local leaders, district registrars and people should be implemented for better understanding of the issue.