Chylothorax is an uncommon but serious medical condition, which arises when intestinal lymphatic fluid leaks into the pleural space. Treatment strategies depend on the daily output and underlying etiology, which may be due to direct injury to lymphatic vessels or a nontraumatic disorder. Chest radiographs confirm the presence of pleural fluid and lateralize the process. In the setting of direct injury, lymphangiography can often be both diagnostic and facilitate a minimally invasive attempt at therapy. CT and MRI in this setting may be appropriate for cases when lymphangiography is not diagnostic. When the etiology is nontraumatic or unknown, CT or MRI can narrow the differential diagnosis, and lymphangiography is useful if a minimally invasive approach to treatment is desired. The American College of Radiology Appropriateness Criteria are evidence-based guidelines for specific clinical conditions that are reviewed annually by a multidisciplinary expert panel. The guideline development and revision include an extensive analysis of current medical literature from peer-reviewed journals and the application of well-established methodologies (RAND/UCLA Appropriateness Method and Grading of Recommendations Assessment, Development, and Evaluation or GRADE) to rate the appropriateness of imaging and treatment procedures for specific clinical scenarios. In those instances where evidence is lacking or equivocal, expert opinion may supplement the available evidence to recommend imaging or treatment.