Lack of efficacy of conventional treatments of obesity has led to increasing popularity of bariatric surgery as a therapeutic option. Little is known about possible long-term effects. Although an increased incidence of peripheral neuropathy after surgery has been reported, there is an absence of good prospective evidence. The aim of this prospective study was to objectively assess peripheral and autonomic nerve function in subjects before and 1 year after bariatric surgery. 10 subjects (9 females) had detailed quantitative sensory testing, nerve conduction studies (radial, sural, common peroneal and tibial nerves), and autonomic function tests. Sensory nerve conduction velocity (SNCV) fell by 15% from 67.79±7.6 to 57.4±2.9m/s (mean±SD) in the radial nerve(p<0.005) and by 20% from 52.6±6.1 to 42±5.6m/s in the sural nerve(p<0.0001). This was accompanied by a rise in amplitude in both nerves (radial nerve: 43.9±11.4 to 56.3±17.6µ V, p=0.1; sural nerve: 15.6±4.8 to 22.5±11.0µ V, p<0.05). No significant changes were seen in parameters of motor nerve function or quantitative sensory testing. Autonomic function testing showed a fail in the resting heart rate from 79.4±10.0 to 68.0±9.2 beats/min(p=0.01) and a rise in beat-to-beat variation OUR ratio) on standing from 1.32±0.2 to 1.51±0.2(p<0.002). N other significant changes were noted in autonomic function. This study shows a large decline in SNCV after bariatric surgery. Substantial reductions in body fat may be having an impact on the composition of myelin, a major determinant of SNCV, which consists of 70% lipid. The role of nutritional deficiencies after surgery, as well as inflammatory and immune mechanisms also deserves consideration. The improvements in sensory nerve amplitude are probably due to improved signal detection as a result of reductions in subcutaneous fat. Bariatric surgery is increasingly being employed to treat obesity. It is clear, however, that sensory nerve dysfunction is common sequelae and may herald the development of more overt peripheral neuropathy. [ABSTRACT FROM AUTHOR]