Diagnostic testing for determining the sources of neuropathic pain has evolved over time. Good clinical practice requires that the clinician takes a good history and performs an appropriate clinical examination to establish the diagnosis of neuropathic pain as possible or probable. Quantitative sensory testing (QST) is helpful in the early diagnosis and follow-up of peripheral neuropathy affecting small-fiber function. Peripheral nerve biopsy was performed in certain circumstances, such as when vasculitis, amyloid, or an unspecified inflammatory condition could be the etiology of peripheral neuropathy. Computerized tomography (CT) and magnetic resonance imaging (MRI) scans can facilitate diagnoses by identifying causes of central and peripheral nervous tissue ischemia, demyelination, compression, or infiltration. Functional MRI works on the principle that regional cerebral blood flow (rCBF) is related to regional cerebral activity. Autonomic function testing relies on indirectly accessing the function of unmyelinated postganglionic fibers, which cannot be tested directly by conventional neurophysiological techniques.