HISTORY: A 20 year female student/runner reported one month history of lateral leg, foot, and toe numbness. The symptoms began as she increased her running mileage for marathon training. She noted difficulty with walking, tripping with occasional falls, intermittent pain at her fibular head, and "pins and needles" in her lateral calf. PHYSICAL EXAMINATION: The patient's Lower Quarter Screen showed diminished sensation to the R lateral leg and great toe, decreased strength of R foot and ankle, an inability to heel walk, and difficulty toe walking. Sensation was absent to 10-mg monofilament testing in the peroneal nerve distribution. MMT grades were as follows: Ant Tib 3/5, Post Tib 3+/5, Peroneals 3+/5, EHL 2+/5, FHL 4/5, FD 3/5. Gait showed increased knee flexion, limited dorsiflexion, and increased extensor digitorum activity on the R in swing phase. Joint play was hypomobile at the proximal and distal anterior tibio-fibular joint. Supine SLR test was + for pain near the fibular head and lateral calf tingling. DIFFERENTIAL DIAGNOSIS: mass lesion; acute compartment syndrome; lumbar radiculopathy; peroneal neuropathy TEST AND RESULTS: EMG findings showed a complete conduction block of the peroneal nerve at the fibular head. FINAL WORKING DIAGNOSIS: Idiopathic peroneal neuropathy TREATMENT AND OUTCOMES: The pt. began PT 3x/wk for proximal and distal anterior tibio-fibular joint mobilizations, anterior taping of the fibular head, peroneal nerve glides, NMES of the dorsiflexors/evertors, a dorsiflexion assist taping, and a HEP for ankle and toe strengthening. After 2 months, tibio-fibular joint mobility was normalized and neural gliding was discontinued. Strength was improving but sensation remained absent. Treatment was decreased to 1x/wk for selective muscle strengthening including: active-assisted ROM, multi-angle isometrics, and eccentric strengthening. One month later pt. was released to a HEP and FAAM scores were recorded: ADLs 64%, Sport 0%. Monthly follow-ups continued until pt. discharged from PT 9 months after eval. Complete resolution of symptoms occurred 10 months after symptom onset. At discharge sensation was intact to 10-mg monofilament testing, strength was 5/5 in the foot and ankle, gait was normalized, and FAAM scores were 100% in ADLs and Sports. The pt. was running 6-10 mi/day, 6 days/week.