Introduction: Thoracic ultrasound (TUS) is increasingly used in chest medicine in secondary care. The indications for TUS are well known but less is known about their relative frequency. The purpose of this observational study was to describe the common indications for TUS and their relative frequency and the impact of TUS on management in a consecutive group of patients. Methods: 80 consecutive inpatients and outpatients referred for TUS by the same operator in a UK National Health Service teaching hospital were included. Demographic data, clinical indication, findings and effect of TUS on clinical management were noted. Results: The most common clinical indication was to assess a pleural effusion in 60/80 cases (75%), but other indications included assessment of diaphragmatic function, pleural thickening and chest wall masses. TUS significantly altered patient management in 52/80 cases (65%): it resolved equivocal chest radiograph (CXR) findings and excluded pathology in 20/80 cases (25%), detected effusions not visible on CXR in 14/80 cases (18%), localised a safe site for medical thoracoscopy in 11/80 cases (14%) when not clinically apparent, and detected unexpected septation in 7/80 cases (9%). TUS guided pleural cytology diagnosed pleural fluid metastases in 9/22 cases aspirated (41%). Conclusion: There are many clinical indications for TUS but the most common is pleural effusion assessment. TUS can diagnose inoperable pleural metastases, allow safe day case pleural intervention, exclude significant pleural pathology not visible on CXR, and triage further investigation.