An electrical stimulation system for treatment of erectile dysfunction in a patient, the system comprising: an implantable stimulation unit comprising: an array of electrodes disposed on at least one flexible substrate sized and shaped to abut at least a portion of a pelvic plexus of a patient; a programmable controller operatively coupled to the array of electrodes, the programmable controller including a stimulation circuit, a nonvolatile memory and a microprocessor coupled to the stimulation circuit and the nonvolatile memory, wherein the nonvolatile memory stores an identity of an empirically determined subset of the array of electrodes post implantation of the implantable stimulation unit and a stimulation routine used by the microprocessor to supply electrical stimulation via the stimulation circuit and the pelvic plexus to at least one cavernous nerve sufficient to cause an erection; and an external patient controller configured to selectably activate the implantable stimulation unit responsive to a patient input; and an external physician controller configured to selectively activate desired subsets of the array of electrodes to determine the empirically determined subset of the array of electrodes post implantation of the implantable stimulation unit and to cause the nonvolatile memory of the implantable stimulation unit to store the stimulation routine used by the microprocessor post implantation of the implantable stimulation unit. an implantable stimulation unit comprising: an array of electrodes disposed on at least one flexible substrate sized and shaped to abut at least a portion of a pelvic plexus of a patient; a programmable controller operatively coupled to the array of electrodes, the programmable controller including a stimulation circuit, a nonvolatile memory and a microprocessor coupled to the stimulation circuit and the nonvolatile memory, wherein the nonvolatile memory stores an identity of an empirically determined subset of the array of electrodes post implantation of the implantable stimulation unit and a stimulation routine used by the microprocessor to supply electrical stimulation via the stimulation circuit and the pelvic plexus to at least one cavernous nerve sufficient to cause an erection; and an array of electrodes disposed on at least one flexible substrate sized and shaped to abut at least a portion of a pelvic plexus of a patient; a programmable controller operatively coupled to the array of electrodes, the programmable controller including a stimulation circuit, a nonvolatile memory and a microprocessor coupled to the stimulation circuit and the nonvolatile memory, wherein the nonvolatile memory stores an identity of an empirically determined subset of the array of electrodes post implantation of the implantable stimulation unit and a stimulation routine used by the microprocessor to supply electrical stimulation via the stimulation circuit and the pelvic plexus to at least one cavernous nerve sufficient to cause an erection; and an external patient controller configured to selectably activate the implantable stimulation unit responsive to a patient input; and an external physician controller configured to selectively activate desired subsets of the array of electrodes to determine the empirically determined subset of the array of electrodes post implantation of the implantable stimulation unit and to cause the nonvolatile memory of the implantable stimulation unit to store the stimulation routine used by the microprocessor post implantation of the implantable stimulation unit.