Cauda equina syndrome(CES) and disc rupture have been implicated as a potential complication of spinal manipulation. A review of the literature from 1911 to 1996 received 61 reported cases of cauda equina syndrome or disc rupture in patients undergoing manipulation. This article presents four new cases, where a temporal association was found between the onset of cauda equina symptoms or disc rupture and lumbar manipulation. The type of manipulation administered and the relationship between the treatment and symptoms is reviewed. Our patients symptoms suggest that acute herniation was caused, or at least precipitated by spinal manipulation. In each of these cases the chiropractitioner failed to comprehend the nature of the problem and take appropriate action. As a consequence, the patient went untreated for several days. Many chiropractic therapists assumed the incidence of CES caused by manipulation to be approximately one in many millions of treatments. However, we assumed that CES or disc rupture is far more common than the literature would reflect. It is therefore essential that persons practicing or prescribing manipulation would be aware of these complications.