Although various postoperative complications can occur after lumbar spine surgery, acute appendicitis remains relatively uncommon. Prompt identification and timely intervention for such complications are crucial for optimizing patient outcomes. A 55-year-old Persian woman with a body mass index of 35 kg/m2 presented with lower back pain radiating to her right leg. Magnetic resonance imaging revealed lumbar canal stenosis and L3–4 spondylolisthesis. She underwent an L3–4 laminectomy and transforaminal lumbar interbody fusion, which were completed without any immediate complications. However, postoperatively, she developed progressively worsening abdominal pain, necessitating exploratory laparotomy. This procedure identified acute appendicitis with a fecalith, requiring an appendectomy. This rare case underscores the importance of recognizing acute appendicitis as a potential complication following lumbar spine surgery, especially in obese patients. Early diagnosis and intervention are essential to achieve favorable outcomes. Reporting such cases helps raise awareness among healthcare professionals and contributes to evidence-based improvements in clinical practice.