Because of the clinical implications of Human Immunodeficiency Virus (HIV) status on treatment of tuberculosis (TB) and in view of the low percentage of patients in whom HIV testing is performed, we evaluated immunological features of 54 patients with newly diagnosed TB and its ability to predict HIV co-infection. All 54 patients had initially unknown HIV status and had no other Acquired Immunodeficiency Syndrome (AIDS) defining illnesses. Twenty-two patients were found to be HIV seropositive and 32 were seronegative. The median CD4 and CD8 counts were statistically different between the HIV seropositive and seronegative patients, however, there was overlap between the two groups. The median CD4:CD8 ratio was 0.17 in HIV seropositive patients and 1.95 in the seronegative patients and had minimal overlap (p < 0.0001). A CD4:CD8 ratio < or = 0.7 gave a sensitivity of 100%, specificity of 94%, positive-predictive value of 92% and a negative-predictive value of 100% in predicting HIV co-infection. In conclusion, HIV-co-infection in patients with newly diagnosed TB could be predicted on the basis of the CD4:CD8 ratio.