This paper generalizes the theory of irreversible investment under uncertainty by allowing for risk averse investors in the absence of com-plete markets.Until now this theory has only been developed in the cases of risk neutrality, or risk aversion in combination with complete markets.Within a general setting, we prove the existence of a unique critical output price that distinguishes price regions in which it is optimal for a risk averse investor to invest and price regions in which one should refrain from investing.We use a class of utility functions that exhibit non-increasing absolute risk aversion to examine the e ects of risk aversion, price uncertainty, and other parameters on the optimal investment decision.We nd that risk aversion reduces investment, particularly if the investment size is large.Moreover, we nd that a rise in price uncertainty increases the value of deferring irreversible investments.This e ect is stronger for high levels of risk aversion.In addition, we provide, for the rst time, closed-form comparative statics formulas for the risk neutral investor.