With relational contracts, increased uncertainty with no change in factor prices is shown to reduce investment in the long run even if the parties are risk neutral. This contrasts with models based on the impact of financial risk on the cost of capital and on the option value arising from irreversible investment. For the latter, Bloom et al. (Econometrica, 2018) find that a negative first-moment shock, in addition to increased uncertainty, best matches the data. This paper develops a relational contract model to demonstrate the impact of uncertainty on investment, depending on whether investment is general or specific. It then uses a specification calibrated with parameters from Bloom et al. (Econometrica, 2018) to show that this model can generate effects on productivity and investment of the magnitude of the negative aggregate shock in that paper purely with an increase in uncertainty.