Acute appendicitis in children under 5 years of age is a diagnostic challenge, its delay is usually dramatic and leaves serious sequelae. It is one of the main causes of surgical intervention, it is common for other diseases to be associated with it and to simulate it. Acute appendicitis is of obstructive etiology and its pathophysiology, the bacteriology involved and the evolution of the disease progresses through its phases, from the simple to the complex, is addressed in each case. The typical abdominal pain of appendicitis, in addition to vomiting and fever at a young age, is most often accompanied by an atypical clinical picture such as diarrhea. Integrating the clinical signs at this age requires the full capacity and good sense of the pediatric surgeon. For a correct and timely diagnosis, unfortunately many pediatric patients present in complicated stages of the disease, which implies decision-making regarding the type of surgical intervention and subsequent treatments.