Leg pain is a frequent accompaniment to low back pain, arising from disorders of neural or musculoskeletal structures of the lumbar spine. Differentiating between different sources of radiating leg pain is important to make an appropriate diagnosis and identify the underlying pathology. It is proposed that low back-related leg pain be divided into four subgroups according to the predominating pathomechanisms involved. The first subgroup features central sensitization with mainly positive symptoms such as hyperalgesia, the second subgroup involves denervation with significant axonal damage showing predominantly negative sensory symptoms and possibly motor loss and the third subgroup involves peripheral nerve sensitization with enhanced nerve trunk mechanosensitization. The fourth subgroup features somatic referred pain from musculoskeletal structures, such as the intervertebral disc or facet joints. Accordingly, four groups of patients with leg pain associated with structures in the lower back can be identified: Each group presents with a distinct pattern of symptoms and signs. Although there may be considerable overlap between the classifications, the authors propose the existence of an overriding mechanism. The importance of distinguishing low back-related leg pain into these four groups is to facilitate diagnosis and provide a more effective, appropriate treatment.