The diagnosis and treatment of failed lumbar spinal surgery remains controversial. The differential diagnosis is based on the pattern of pain distribution and the time interval between surgery and the onset of symptoms. Of the many causes of failure after lumbar fusion, the most common is pseudarthrosis. This article reviews the surgical treatment of pseudarthrosis as a primary cause of failed lumbar surgery. Despite advances in surgical technique and internal fixation methods, nonunion remains a problem after pseudarthrosis repair even when the original indication for fusion was clear-cut.