Treatment of anastomotic fistulas generally implies an individualized concept. The origin of these complications is multifactorial and comprises such factors as primary operation, oncologic situation, comorbidity, and patient age as well as fistula-specific considerations such as anatomic localization, secretion volume, etc. In the case of high-output fistulas, it is of great importance to counteract fluid and electrolyte imbalances. Furthermore, skin maceration due to aggressive secretion needs to be averted. Therapeutic options include operative and endoscopic interventions. Octreotide plays a role in high-output and pancreatic fistulas. Any underlying ailment (e.g., Crohn's disease) requires an optimal disease-specific treatment which characterizes an interdisciplinary approach to such fistulas. The following article discusses general and site-specific considerations in the diagnosis and treatment of anastomotic fistulas.