This clinical reference manual, Diagnostica medica differenziale, by Aminta Fieschi, reached its third edition in 1958, indicating its consolidation in Italian internal medicine and clinical diagnostics. The first volume focuses on the differential diagnosis of symptoms and syndromes, guiding practitioners in distinguishing between diseases with overlapping clinical presentations. Structured by organ systems and symptom categories, it reflects the mid-20th-century Italian medical curriculum, with an emphasis on bedside diagnostics, observational methods, and case-based reasoning. It served as a foundational tool for medical students, general practitioners, and clinicians navigating complex diagnostic scenarios.