Percutaneous laser disc decompression (PLDD) is an effective method of treating the lumbar herniated nucleus pulposis (HNP) that is both contained by the annular/posterior longitudinal ligament (PLL) complex and connected to the parent disc of origin. Not all radiological studies have the same ability to diagnose this specific type of herniation and therefore are not equally useful in the preoperative evaluation of the PLDD candidate. Ninety PLDD treated patients were retrospectively reviewed to determine which of the four most commonly performed lumbar imaging exams, when abnormal, correlated with a successful outcome. Overall MacNab criteria improvement occurred in 73.3% of PLDD-treated patients. An abnormal CT discogram correlated with PLDD success in all patients treated (100%). An abnormal MRI, CT, or myelogram correlated with success in 75% or less of patients treated. The theoretical reasons for the superiority of CT discography are discussed and the diagnostic potential of all major lumbar imaging modalities is reviewed. A diagnostic decision scheme for the evaluation of the prospective PLDD patient is presented.