We investigate whether giving workers autonomy through delegation of contract choice intrinsically motivates effort. In a novel laboratory experiment that controls for contract preferences and outcomes, principals can either choose the contract under which agents work on a real-effort task, or delegate the contract choice to the agents. We evaluate whether agents exert higher effort when they are allowed to choose the contract versus when the contract is imposed on them. We find no difference between the two conditions, even after controlling for baseline ability and for locus of control. Because our design excludes the possibility that preferences play a role, and because workers engaged in a real-effort task, this result casts doubt on an intrinsic link between the autonomy granted through delegation and the motivation of employees in the workplace. Our results do not deny, however, the possible instrumental benefits of autonomy (which did not play a role in our design) and their potentially powerful impact on motivation.