This article explores the link between trust and law through the prism of the mafia phenomenon. Mafias spread in a context of “endogenous mistrust” and manage to privatize law by imposing an unwritten system of rules in their territory. This alternative system of law has consequences in terms of distorted access to economic opportunities for non-Mafiosi as it is oriented in favor of its affiliates and external backers. It also leads to the emergence of negative social capital benefiting Mafiosi but unable to create relationships based on genuine trust.