The disclosure describes blood flow sensors for detecting penile tumescence. A system according to the invention may include at least one sensor for sensing blood flow into the penis, and one sensor for sensing blood flow away from the penis. Detecting penile tumescence may be accomplished by comparing the flow of blood into the penis to the blood flow out of the penis. A greater inflow of blood indicates an increasing tumescence whereas a greater outflow of blood indicates a decreasing tumescence. The sensors may be used for short- or long-term monitoring of penile tumescence, or as closed-loop feedback in a therapeutic penile tumescence control system, which may deliver electrical or chemical stimulation therapy to control a tumescence or erectile state, thus treating sexual dysfunction or, more specifically, erectile dysfunction.
