Aim of work: To study the diagnostic value of ultrasound guided biopsy in patients with malignant pleural effusion. Patients and methods: This study involved 40 patients with malignant pleural effusion of indeterminate aetiology. All patients had a contrast CT chest performed and were divided into 3 Groups according to their radiologic appearance: GROUP 1: 10 patients having pleural effusion only. GROUP 2: 15 patients having pleural effusion and pleural thickening. GROUP 3: 15 patients having pleural effusion and pleural mass lesions. All 3 groups of patients underwent ultrasound examination in the Radiology department. In patients of Groups 2 and 3, ultrasound fluid aspiration and ultrasound guided core biopsy of the pleura were attempted. Patients of all 3 Groups performed Medical thoracoscopy in the interventional pulmonology unit. Results: In Group 1 patients, US guided biopsy was contraindicated and could not be performed due to absence of pleural thickness, nodulation or masses. Thoracoscopy was performed in them all with a sensitivity reaching 90%. In Group 2, a malignant aetiology was reached in 5/10 cases whom had adequate tissue retrieval (sensitivity 50%). In Group 3, 12/15 patients were diagnosed by US guided biopsy (sensitivity 80%). The mean sensitivity of US guided biopsy in both Groups was 65%. Thoracoscopy was then performed successfully in all of patients in Groups 2 and 3 with a diagnostic sensitivity of 100% each. The mean diagnostic sensitivity of thoracoscopy for all 3 Groups was 96.7%. Conclusion: The US guided pleural biopsy with a Tru-cut needle is simple, safe and well tolerated. It is especially useful for patients with pleural tumour, thickened pleura, small amounts of pleural effusion or loculated pleural effusion.