Objective To assess the effectiveness and safety of collagenase for intervertebral disk hernia, to facilitate the rational selection of the most appropriate therapy. Methods We searched the following electronic databases: Medline (1966 to May 2006), EMbase (1966 to May 2006), The Cochrane Library (Issue 2, 2006), CRD (Center for Reviews and Dissemination, York University), CBM (1978 to May 2006), CNKI (1994 to 2006), and VIP (1989 to 2006). RCTs or quasi-RCTs were included. RevMan 4.2 was used for statistical analysis. Results Six RCTs and one quasi-RCT involving 829 participants were included. One study showed that the short-term effective rate was similar between chemonucleolysis (CNL) and percutaneous laser dise decompression (PLDD), but the long-term effective rate of PLDD was superior to that of CNL (RR 0.35, 95%CI 0.13 to 0.96). One study revealed that the short- and long-term effective rate of CNL were higher than those of placebo (Plt;0.05). Two studies comparing collagenase vs chymopaain were heterogeneous: one indicated that chymopapain was superior to collagenase according to ITT analysis (Plt;0.05); but the other revealed no significant difference among the high- and low-dose collagenase groups and chymopapain group (Pgt;0.05). One trial showed that the effective rate between collagenase and automated percutaneous lumbar discectomy (APLD) was not significantly different (Pgt;0.05). The overall results of CNL vs Triamcinolone Acetonide showed no significant difference, but significant difference was found among patients with different types of intervertebral disk hernia. One study showed that CNL was superior to Prednisolone. Three studies reported adverse effects, mainly involving pain, neurologic deficit, cauda equina syndrome and allergic reaction amongst others. Conclusions No adequate evidence shows which therapy is more effective for intervertebral disk hernia. More high-quality trials are required.