Tuberculosis (TB) is one of the most worrying infectious diseases facing less developed countries. Diagnosis and treatment of those who are transmitting Mycobacterium tuberculosis is considered a very effective control strategy. Within this strategy the priority is to achieve high cure rates before attempting to increase case finding. However, there is a dearth of research on how to increase case finding and diagnostic coverage in those settings where high cure rates are being achieved. This paper presents an evaluation of the impact on case finding of a mass media health education campaign for TB control in Cali, Colombia. The campaign aimed at increasing case finding and reducing levels of prejudice against people with TB. The impact assessment shows that the campaign produced an increase of 64% in the number of direct smears processed by the laboratories and an increase of 52% in the number of new cases of positive pulmonary TB, with respect to the previous period. Unfortunately, the effects of the campaign were short-lived. These findings have at least two important implications. First, passive case finding is likely to be an insufficient strategy to reach the operational targets of diagnostic coverage. Secondly, providing basic information about the earliest symptoms of TB and the procedures for diagnosis can increase diagnostic coverage, and thus strengthen the effect on infection risk of control programmes with high cure rates. Further research is required to identify other strategies that could, first, increase diagnostic coverage and, secondly, make the intervention effects sustainable.