The ulnar dorsal aspect of the hand is predominantly innervated by the dorsal ulnar cutaneous nerve with variable input from the superficial radial cutaneous nerve. This cross innervation can cause difficulty in interpreting low amplitude sensory nerve action potential for the dorsal ulnar cutaneous nerve particularly when facing suspected ulnar neuropathyat the elbow. In three subjects with low dorsal ulnar cutaneous sensory nerve action potential amplitude due to cross over with the superficial radial nerve, we compared amplitude with nerve circumference and fascicular count as measured by ultrasound. Dorsal ulnar cutaneous nerve circumference was significantly smaller where there was low sensory nerve action potential amplitude and showed fewer fascicles. Nerve ultrasonography may be a useful additional test modality to determine if low dorsal ulnar cutaneous nerve amplitude is physiological.