Objective.-Ulnar nerve compression, the Guyon's canal syndrome, is more unusual than carpal tunnel disorders. An exceptional case of a patient with vascular and neurogenic signs and symptoms is described.Patient Presentation.-A 26-year-old female physiotherapist presented with neurogenic and arteriovenous signs and symptoms involving the right hand. The patient described fourth fi nger and wrist pain with fl exion, and pain and itching extending to arm and forearm. Sensations worsened when exposed to air conditioning. Enlarged vessels were noted in the medial aspect of the fourth digit; trauma occurred 8 years earlier during attempts to open a nail polish container.Methods.-Color fl ow, duplex-Doppler ultrasonography (US) of the subclavian to digital vessels was performed using 3-to 13-MHz transducers. Interpretation focused on fl ow waveforms obtained with the hand open and closed, having the left extremity as reference. Thermography was performed with camera Flir 15, room temperature at 21°C (70°F) and relative humidity at 48%.Results.-Right subclavian to digital arteries had high diastolic fl ow with opened hand. Hand closure interrupted diastolic fl ow except in the ulnar circulation to the fourth digit. Common digital arteries feeding digits 3-4 and 4-5 had signifi cantly more diastolic fl ow than the artery feeding digits 2-3. Diastolic fl ow through a dilated ulnar artery despite hand closure was associated to a millimetric arteriovenous fi stula in the fourth fi nger. Hyperthermia saturating at 35°C (95°F) showed channel-like images over the ulnar nerve and artery and fourth digit, compared with 20°C (68°F) for digit 2.Conclusions.-US and thermography demonstrated high fl ow and hyperthermia associated with a fourth digit fi stula and abnormal vessels, and ulnar artery dilatation likely associated with ulnar nerve injury. A coadjuvant diagnosis of Guyon's canal syndrome at the wrist was raised.