Objective To reassess the utility and validity of ultrasound (US) screening in infants with lumbar midline skin stigmata (MSS) that may be associated with tethering of the spinal cord. Study design We conducted a prospective observational study of 254 infants under age 6 months with suspicious dorsal MSS between 2005 and 2007. All infants were examined by US and neurosurgical clinical evaluation, and 50 infants also underwent magnetic resonance imaging (MRI). The US and MRI findings were analyzed for correlation. Associations between the imaging findings and the presence of the low-risk skin lesions simple dimple (113 cases) and deviated gluteal fold (DGF; 44 cases) also were evaluated. Results Analysis of US and MRI results for the cohort of 50 neonates in whom both examinations were performed showed high concordance. The low-risk group of infants with simple dimple and DGF constituted 157 US procedures, 96% of which were of high quality, providing clear visualization of spinal components. None demonstrated any clinically significant pathological findings. Conclusions Our data reaffirm the reliability of US as a screening tool for tethered cord syndrome. Infants with low-risk lesions, such as simple dimple and DGF, may be absolved from US screening, because these findings alone do not indicate underlying pathological lesions. We propose a simplified diagnostic classification system for MSS.