This paper describes the preliminary performance of a surgically implanted neuroprosthesis for standing and transfers after spinal cord injury (SCI) in an initial group of 12 volunteers with longstanding paralysis. The CWRU/VA standing neuroprosthesis consists of an 8-channel implanted receiver-stimulator, epimysial and surgically implanted intramuscular electrodes, and a programmable wearable external controller. After reconditioning exercise and rehabilitation with the system, most individuals with paraplegia or low tetraplegia were able to stand, transfer, and release one hand from a support device to manipulate objects in the environment or to perform swing-to ambulation in a walker. The effort and assistance required for transfers were reduced for users with mid-level tetraplegia, although the maneuvers were not independent. Neuroprosthesis users with tetraplegia and paraplegia alike benefited from the improvements in their general health derived from exercise, including reduced risk of decubiti and self-reported modulation of spasticity. Stimulated responses are stable and sufficiently strong for function, and implanted components are reliable with a 90% probability of epimysial electrode survival at 4 years post-implant. The techniques employed are repeatable and teachable, and suitable for multi-center clinical trial.