According to the Jack-of-all-trades theory, people with a balanced set of skills are more suitable for self-employment than are those without. In this paper we test this theory using Swedish Military Enlistment data. This data enables us to construct a measure of balance in abilities that, in comparison to measures used in previous research, is less contaminated by endogeneity problems. We find clear support for the Jack-of-all-trades theory, in the sense that the likelihood of being self-employed is higher for individuals whose skills are balanced. In addition, their earnings from self-employment tend to be higher.