Introduction: Palmaris brevis spasm syndrome (PBSS) is spontaneous, involuntary contractions of the palmaris brevis (PB) muscle. Here, we aim to examine origin of the contractions in four patients diagnosed as PBSS. Methods: Clinical, neurological and electrophysiological findings, information regarding demographics, and treatment details of PBSS patients were assessed. Routine electrophysiological and polymyographic investigations, cervical magnetic resonance imaging, and roentgenograms of the wrist and elbow were studied. To clarify the origin of the involuntary activity, (1) we compressed ulnar nerve with ice bags over the wrist and over the hypothenar region for 10 minutes, (2) we compressed ulnar nerve for 10 minutes by bare hands at the level of wrist, (3) we induced 10-minutes ischemia of the affected arm produced by suprasystolic cuff compression at the upper arm, (4) we injected 10 ml lidocain in the midpoint of the line between medial epicondyle of humerus and olecranon process of ulna, and (5) we injected botulinum toxin type A into the PB muscle. Results: Polymyographic electromyography revealed bursts of frequently recurring motor unit potentials over PB muscle. None of the applications except botulinum toxin changed the contractions. The only way to suppress the contractions was botulinum toxin injection. Discussion: PBSS likely originates from the most distal part of the nerve and botulinum toxin is the choice of treatment.