Using retrospective data, we introduce evidence that occupational exposure significantly affects disability risk. Incorporating this into a general equilibrium model, social disability insurance (SDI) affects welfare through (i) the classic, risk-sharing channel and (ii) a new channel of occupational reallocation. Both channels can increase welfare, but at the optimal SDI they are at odds. Welfare gains from additional risk-sharing are reduced by overly incentivizing workers to choose risky occupations. In a calibration, optimal SDI increases welfare by 2.6% relative to actuarially fair insurance, mostly due to risk sharing.
