Tuberculosis (TB) is a global public health concern, specifically in countries which have high prevalence of HIV/AIDS, malnutrition, unhygienic conditions, etc. Some evidence has been presented that diabetes mellitus (DM) is a risk factor for TB. On the other hand, among those who have DM, TB infection enhances glucose intolerance and worsens glycemic control. The combination of TB and DM, due to immuno-compromised status of DM, can delay the healing process of TB. The focus of this paper is the World Health Organization directly observed treatment, short course (DOTS) program implemented in Gazan province, Saudi Arabia, to treat TB. The data included some patients with both TB and DM. The data has been analyzed to assess how effective the DOTS program was in managing TB. It was found that DM was not a significant factor in the outcome of TB treatment. We used the same data and observed that the non-significance of DM is due to heterogeneity of patient population, Saudis and Non-Saudis. The prevalence of DM was very high among Saudis. This is understandable in view of different lifestyles. Non-Saudis are predominantly Yemenis. For Saudis, DM was indeed found to play a role in the treatment outcome of TB, after an application of a classification tree methodology on the data. This is the main focus of the paper.