In this clinical lesson we present two patient cases. A 66-year-old female patient with a clinical, biochemical and radiological suspicion of complex appendicitis. The patient undergoes an appendectomy and post-operative recovery is beset with complications. The other case involves a 24-year-old male patient with suspected simple appendicitis. He is successfully treated with antibiotics and without surgery. By using these patients as examples, we discuss the revised clinical guideline for diagnosing and treating acute appendicitis. Besides that, we also discuss the differentiation between simple and complex appendicitis and how this can influence the treatment plan.