The aim of this study was to validate the Italian version of the Neuropathic Pain Symptom Inventory (NPSI) in patients with neuropathic pain due to peripheral nerve diseases, and also to evaluate the validity of a new NPSI score: a frequency weighted NPSI score (NPSI-FW). First, the original version of the NPSI was translated into Italian. Then the validity and reliability of the Italian NPSI (I-NPSI) were tested in 392 Italian patients consecutively referred to 16 Italian outpatient services for peripheral nerve diseases, by correlating the I-NPSI scores with other pain scales. The repeatability and responsiveness were assessed. A significant correlation between the I-NPSI scores and all the other pain measures was seen. Reproducibility and responsiveness were good. Our study shows the validity of the I-NPSI and demonstrates its reliability for assessing neuropathic pain in patients with peripheral nerve diseases. The I-NPSI scores represent reliable measurements to assess neuropathic symptoms and effectiveness of treatment on them.