The posterior interosseous nerve palsy is a neuropathy of radial nerve interesting its deep motor branch. The neuropathy can appear with a hollow in the proximal half of the forearm without significant swelling, a complete loss of extension of the fingers with radial deviation of the wrist during extension. In some cases, PIN compression may simulate tendon rupture in rheumatologic diseases, because the pain and the paralysis occur suddenly, so often can be difficult to make a diagnosis. The palsy is caused by compression of the posterior interosseous nerve from soft tissue tumours or tumour-like masses: ganglions, lipomas, rheumatoid synovitis, synovial chondromatosis, fibromas, neurofibromas, bursitis, synovial cysts of the elbow and radioulnar proximal joints. The aim of our research was to individuate the better treatment for the posterior interosseous nerve palsy.From 2002 to 2007 we examined 8 patients: 2 female and 6 male. Median age was 43 years. The diagnosis was made by clinical examination, ultrasound, nerve conduction studies and magnetic resonance imaging (MRI). Patients underwent to decompressing posterior interosseous nerve surgery.After the surgical exploration in 8 cases a globular mass of around 2.5 cm to 4.5 cm diameter was discovered. At the histological examination, a synovial cyst of the elbow joint was found in 7 out of 8 patients and an hemangioma tumor in the one remaining patient. 12 months was the median time for a complete recovery after the operation, confirmed by EMG.The surgical treatment offers a complete resolution in all cases.