An epidemiological study of tuberculosis infection in the Kingdom of Saudi Arabia was conducted, between January 1987 to February 1990. A proportional to population size sampling method was used for the whole country, and 1933 subjects were screened. A pre- designed questionnaire was used to collect details of BCG scar, age, sex, residence area, nationality, education, occupation and tuberculosis test. The relative importance of these factors was assessed by using Logistic Regression Analysis. The extent to which these factors affected the severity of tuberculosis was also examined. A number of statistically significant association were found between positive tuberculin test (> 10mm) and age (p < 0.0001), sex (p = 0.018), nationality (p = 0.009), residence area (p = 0.05) and occupation (p = 0.0003).