Anomalies of the flexor digitorum superficialis muscle are extremely uncommon and usually present as a mass or pseudotumor within the palm. First described by MacAlister (1868) in postmortem dissections, this anomaly can pose a diagnostic and therapeutic dilemma. Most patients complain of a tender mass within zone II or III of the palm which increases in size with physical activity. Magnetic imaging resonance (MRI) may be useful in defining the extent and characteristics of the mass. Operative exploration and simple debulking will relieve symptoms. To date, there are twenty reported cases and most have involved the right handís small finger flexor digitorum superificialis tendon. We report an additional case in a 17-year-old male where the anomalous flexor digitorum superficialis muscle belly arose from the left handís index finger. To our knowledge, this is the fourth such case reported.