Abstract Background: HIV attacks an immune cell called the CD4 cell. HIV and TB have been closely linked since the emergence of AIDS and TB is the most common infectious disease affecting HIV positive. East and Southern Africa is the hardest region hit by the HIV, this region is the home to 6.2% of the world’s population but it has 19.4 million people living with the virus. The main objective of this study was modeling the determinants of TB status and CD4 cell count among HIV/AIDS patients from HAART in FHTSH. Methods: Longitudinal data was obtained from a sample of 226 HIV/AIDS patients at FelegeHiwot Teaching and Specialized Hospital in north-west, Ethiopia. Two methods of modeling approaches were used those were separate and joint modeling. In the joint model, a LMM and GLMM sub-models were employed together for square root of CD4 cell and TB status respectively. Results: Based on the separate model, the joint models were built to know the correlation between mean change of and CD4 count and TB status overtime. Finally, appropriate model was selected based on AIC and BIC values. The fit statistics showed that, for patient’s age increased by one year, the mean square root of CD4 cell count was decreased by 0.025 cell/mm, 3 controlling other variables constant. The average square root of CD4 cell count for patients whose functional status were ambulatory and bedridden was lower by 3.915 cell/mm 3 and 4.617 cell/mm 3 compared to those who can perform their day to day activity which is working status respectively. The estimated odds of patients being co-infection HIV/TB for who lived in rural area were 3.7 times the estimated odds of those who lived in urban area. The evolution of the association at initial ( ) for the square root of CD4 cell count and TB status was which was essentially the correlation between the two random intercepts. The correlation between the two responses overtime was -0.148. Patients WHO stages, functional status, weight and hemoglobin were significant predictors for both responses. Conclusion: Having lower weight, late WHO clinical stages, non-adhered, opportunity infection disease, lower hemoglobin, being ambulatory and bedridden were associated with higher risk of HIV/TB co-infection and the reduction of CD4 cell count. Therefor there should be a special attention and intervention for HIV positive patients. Keywords: CD4 cell, TB status, Separate Model, Joint Model, HAART