The author analyses the meaning of job security in the present phase labour regulation. This evolution is characterized by a significant increase of flexibility and precariousness of employment, caused by the diffusion of non standard employment relationship (fix term and intermittent). Job security is a value which, according to the Italian Constitution (art. 4), may mean the right of workers to adequate protection against arbitrary dismissal. Art. 18 of the Workers Statute (Act n. 300/1970) guarantees the right of worker illegally dismissed to be reinstated in her/his post: but this provision is considered too rigid and expensive (excessive and unforeseeable firing costs). An accurate analysis of high Courts case law about consequences of illegal dismissals shows a progressive reduction of monetary costs of dismissals (amount of compensation for damages) and the author concludes that the reduction of costs of dismissals diminishes the value of job security.