A patient presented with anterior interosseous nerve syndrome that did not respond to nonoperative treatment. At surgery, nerve compression was found to be from an anomalous fibrous band of the flexor digitorum superficialis extending to the brachialis muscle fascia and separate from the normal arcade passing over the median nerve. Additionally, there was a venous ring encircling the nerve at the level of the anomalous arcade. The patient's muscle weakness recovered after nerve decompression and releasing the anomalous structures.