The incidence and clinical pattern of tuberculous pleural effusion (TPE) and the contribution of individual laboratory procedures in the diagnosis of TPE were assessed in a five year prospective study. Two hundred and fifty-three patients presenting in three participating hospitals with pleural effusion (PE) were assessed clinically and had various laboratory investigations. Eighty-nine (35.2%) of them, including 73 (82%) men and 31 (34.8%) Saudis had TPE. Their mean age +/- SD was 33.4 +/- 11.2 years. Main symptoms in rank order were cough (80%), fever (75%), shortness of breath (64%), chest pain (61%), anorexia and weight loss (47%). PPD was positive in 82 (92%) patients. Positive culture or histological evidence of tuberculosis (TB) was observed in pleural biopsy (68.5%), pleural fluid (10%) and sputum (2%). Pleural fluid microscopy was positive in only one patient, chest radiological features of TB in 3 (3.4%). Six months anti-TB therapy resulted in complete recovery in 86 patients. It is concluded that in this community TPE constitutes over a third of all the causes of PE. The relatively young age of patients reflects the age structure of the indigenous population as well as immigrant workers. PPD, histology and culture of pleural biopsy were the most useful diagnostic tools while pleural fluid and sputum microscopy were unhelpful. The 6-months anti-TB therapy was excellent.