Castor oil, a potent cathartic, is derived from the bean of the castor plant. Anecdotal reports, which date back to ancient Egypt have suggested the use of castor oil to stimulate labour. Castor oil has been widely used as a traditional method of initiating labour in midwifery practice. Its role in the initiation of labour is poorly understood and data examining its efficacy within a clinical trial are limited. This is one of a series of reviews of methods of cervical ripening and labour induction using standardised methodology.