Purpose: The purposes of this study were to examine variations and frequencies of the arborization patterns and communicating branches of the ulnar nerve in the palm, review existing literature, and relate these findings to nerve decompression in the hand and wrist. Methods: The arborization pattern of the ulnar nerve near Guyon canal was examined in 18 cadaver hands and described according to the classification of Murata et al. Communicating branches between the ulnar and median nerves were described according to the classification of Bas and Kleinert. We measured the specific distance from the wrist flexion crease to the origin of the communicating branch and the angle of the communicating branch with the originating nerve. Results: In 13 of 18 hands (72%), a type 1 arborization pattern was found; in 4 hands (22%), there was a type 2 pattern; and in 1 hand (6%), a branching pattern not previously described was found. In 11 of 18 hands (61%), a communicating branch was observed between the ulnar and median nerves. The branch ran from the ulnar to the median nerve (type 1)in 10 hands (56%); the connection was plexiform (type 4)in one hand (5.6%). The communicating branch originated at a median distance of 1 mm from the distal edge of the transverse carpal ligament and had a median angle of 42.5° (interquartile range, 40° to 45°). Conclusions: Variations in arborization patterns of the ulnar nerve and the existence of communicating branches between the ulnar and median nerves in the palm are common and may lead to the atypical distribution of symptoms and unforeseen risks during hand surgery. Clinical relevance: This study provides a comprehensive overview of previous findings and relates these findings to current clinical practice. Knowledge about variations in arborization patterns of the ulnar nerve and communicating branches between the ulnar and median nerves in the palm optimizes diagnoses and minimizes specific surgical risks in hand surgery.