Spigelian hernia, first described at the 18th century, is a rare ventral abdominal hernia occuring through the spigelian fascia. The diagnosis is difficult especially when there is no palpable mass. The case presented here had a spigelian hernia mimicking an incarcerated incisional hernia. This patient had undergone an appendectomy through a right paramedian incision proviously. Three years later she was operated for a suspected incisional hernia. Exploration did not reveal any defects in the external oblique aponeurosis so no further exploration was done. Our operative findings showed also an intact external oblique aponeurosis but when incised a spigelian hernia was observed beneath this structure, which was repaired promptly. A high index of suspicision is necessary for diagnosis both pre and intraoperatively.