This study aimed to evaluate the diagnostic yield and safety of confocal laser endomicroscopy and ultrasound-guided pleural biopsy in diagnosing patients with unknown pleural effusion.

Inclusion Criteria:

• Adult patients with exudative pleural effusion of unknown origin
• Patients with negative pleural fluid cytology results
• Patients diagnosed with a probable malignant pleural effusion but without a definite diagnosis and requiring further pathological evaluation
• Patients who are fully informed of the purpose and method of the study, agree to participate in the study, and sign an informed consent form

Exclusion Criteria:

• Inability or refusal to undergo UGBx
• Patients with any contraindications for pleural biopsy