This article studies the effect of preferences on an individual's optimal choice between insurance demand and self-insurance in a risk context and then in an ambiguous context. The innovative idea in this paper is to introduce ambiguity about the effectiveness of self-insurance to understand the nature of the relationship between insurance demand and self-insurance demand. We show that an increase in risk aversion increases the demand for insurance and decreases the demand for self-insurance. However, when risk is introduced on the effectiveness of self-insurance, we show that the individual still prefers self-insurance to market insurance. We also show that when ambiguity is introduced on the efficacy of self-insurance, the individual always prefers market insurance to self-insurance. Finally, we determine the conditions under which the individual's self-insurance effort is higher or lower under ambiguity than risk.