Tuberculosis (TB) is a leading cause of death from a single infectious disease accounting for over a quarter of avoidable deaths among adults. More than 95% death occur in the developing countries. Currently a third of Worlds population harbour the tubercle bacilli and is at risk for the disease. As such 30 million people will be die from the disease over the next decade. Unfortunately, the epidemiology, clinical manifestation, management and prognosis of TB are radically altered in patients with HIV infection. At present about 12 million persons worldwide are infected with HIV. WHO estimates that nearly 5 million people have already infected with both the HIV and tubercle bacilli and this co-infection accounts to a double catastrophe. In countries with high prevalence of HIV infection, TB cases have been increasing sharply. Among the Asian countries HIV prevalence is the highest in Thailand and TB is still number 1 cause of death among infectious diseases. With in Thailand HIV prevalence is highest in the three upper Northern Provinces where TB cases have been sharply increased in the recent years. This situation made the rationale of our present study with the general objective to determine HIV sero-prevalence in TB patients along with the specific objectives : to determine the current diagnostic profile of TB , -to determine demographic, socio economic and diagnostic factors of TB, -to measure the frequency of HlV in TB patient with respect to demographic, socio-economic and diagnostic factors, and -to determine any relationship between the said factors and HIV seroprevalence in TB patient in Bangkok. A retrospective study was carried out on patients who were attended Central Chest Clinic Bangkok during October 1992 and March 1993. During this 6 months period a total of 1,632 patients were diagnosed as new TB cases. Among these 1,632 cases, 933 patients were voluntary tested for HIV. Out of the 933 cases tested for HIV, 502 cases met the criteria of this study. Data of all the 502 cases were collected from the medical record through a checklist and analyzed by SPSS microcomputer programme. As such 15.7% new TB patients were found HIV seropositive. Diagnostic profile revealed that 299 patients (59.8%) were +ve for both of smear and culture. 35 patients (7X) were smear +ve culture -ve, 37 patients (7.4%) were smear -ve culture +ve and 129 patients (25.8%) were negative for both the smear and culture. Regarding demographic and socioeconomic characteristics of TB all the 502 cases were found Buddhist and Thai nationals. Age, sex, marital status, occupation, educational status, geographic area and monthly family of the patients were found to be dominating risk factor of causation of tuberculosis. Similarly age, sex, marital status, occupation and geographic area showed significant relationship with HIV seropositivity in TB patients. Among the HIV seropositives 75% were in 25-44 years age group compared with 11% in 15-24 year age group and 13.8% in 45 year and above age group (X(2) = 2.3879, df = 3, p-value = 0.0001), 90%. were male and 10% were female (X(2) = 15.0478, df = 1, p-value = 0.001), 56% were unmarried compare with 35% married and 9% divorced/separated (x(1) = 11.3990, df = 2, p-value = 0.0033), 52% were employed as laborer 37% were unemployed and 11% were belonged to all other occupational groups (X(2) = 20.4087, df = 2, p-value = 0.0004), 94% patients were from Urban area and 6% were from semiurban area (X(2) = 14.5739, df = 2, p-value = 0.0006). Educational status and monthly family income of the patients also showed relationship with HIV seropositivity in TB patients. The strong association between demographic and socio economic socioeconomic factors and tuberculosis as well between these factors and HIV seropositivity in TB patients suggested the conclusion that demographic and socio economic factors are significant risk factors for causation of Tuberculosis as well and HIV infection in TB patients. It was also concluded that HIV infection in TB patients has been increasing markedly. It is therefore, recommended that : 1. Awareness abut tuberculosis and HIV infection in TB patient should be strengthened improved and enhanced especially among the low socio economic class of the urban population. 2. All possible measures must be instituted for an early screening of new TB cases and HIV infection in these cases in high risk group. 3. Early initiation of effective chemotherapy and termination after complete treatment and cure for TB.