BACKGROUND: Commonly, a pneumothorax is induced before medical thoracoscopy to facilitate safe entry into the pleural space. OBJECTIVE: Evaluate the use of transthoracic ultrasound to locate a safe entry site for trocar placement during medical thoracoscopy without induction of a preprocedure pneumothorax. METHOD: The study was designed as a prospective cohort study, performed in the setting of a tertiary care hospital with an active interventional pulmonology program. It included 20 consecutive patients referred for medical thoracoscopy. RESULTS: Ultrasound identified entry sites in all 20 patients. All sites were successfully used, despite the presence of adhesions in 3 patients. There were no complications. CONCLUSIONS: Ultrasound could safely and reliably identify entry sites for trocar placement during medical thoracoscopy, even in patients with pleural adhesions. The use of ultrasound may replace the practice of pneumothorax induction before medical thoracoscopy.