Extreme lateral lumbar disc herniation (ELLDH) occurring into and/or outside the intervertebral foramen was encountered in 95 cases amongst 1600 operations for herniated lumbar disc (6%): 43% occurred at L5-S1, 38% at L4-5, 18% at L3-4, and 1% at L2-3. The incidence amongst all herniations at one particular level was 6% at L5-S1, 4% at L4-5, and 18% at L3-4. The clinical presentation varied according to the level of extreme lateral disc herniation, but was not different from the presentation of a classical paramedian herniation occurring one level above. Forty-three patients were investigated with computed tomography (CT) only, 2 with myelography only, and 50 with both. CT always clearly demonstrated the pathology, but some cases are presented to illustrate the differential diagnosis. Myelography was normal in 13 cases; in 27 cases it showed a typical shortening and enlargement of the nerve root sheath which enters the affected intervertebral foramen. At operation, a total facetectomy was performed in 52 patients, a partial facetectomy in 34, and a lateral approach to the intervertebral foramen in 9. The lateral approaches, either paramuscular with retraction of the paraspinal muscles from the midline, or transmuscular by splitting of the paraspinal muscles, are described and illustrated in detail.