Transcranial B-mode sonography (TCS) is a widely available, non-invasive and cost-effective diagnostic instrument. By convention and due to the resolution of the ultrasound waves in proximity of the probe, structures that are close to the midline are assessed from the ipsilateral side whereas structures that are located distant to the midline are examined from the contralateral side. Most data on TCS in disorders associated with insomnia or parasomnias have been evaluated from the movement disorder perspective and did not address diagnosis or differential diagnosis of sleep disorders directly. Some interesting findings indicate that TCS is valuable for the evaluation of sleep disorder patients with suspected restless legs syndrome (RLS), depressive disorder, or rapid eye movement (REM) sleep behavior disorder (RBD). In a patient complaining about disturbed sleep a TCS demonstrating substantia nigra (SN) hypoechogenicity, raphe hypoechogenicity, and red nucleus (RN) hyperechogenicity may help to support a suspected diagnosis of RLS.