The authors investigated the relationship between the type of lumbar disc herniation (471 discs) and the gross anatomy of the posterior longitudinal ligament (PLL) in the lumbar region of 10 cadavers. The size of PLL diminished significantly as the disc level became lower (P < 0.00001), and there are loose attachment of the central area of rhomboidal expansion of PLL. In the upper lumbar region, central or central-lateral herniation with an intact PLL was predominant. The type of disc herniation appeared to be influenced by the width and development of the PLL with a loosely connected central area. In the lower lumber region, posterior-lateral extrusion with a ruptured PLL was predominant. This may be related to the small or poorly developed PLL in lower lumber/lumbosacral region. It is suggested that the type of disc herniation (PLL intact or ruptured) is related to the morphologic variation of PLL.