This article considers principals' assumptions about human nature in Turkey and the relationship between the assumptions held and the leadership style adopted in schools. The findings show that school principals hold Y-type assumptions and prefer a relationship-oriented style in their relations with assistant principals. However, both principals and teachers reported that principals hold X- and Y-type assumptions, and prefer a task-oriented leadership style in their relations with teachers. The findings are concordant with the related literature that (1) a manager who holds theory Y assumptions may tend to adopt a "democratic" leadership style, (2) theory X assumptions may lead a manager to adopt an autocratic style and (3) a leader can adopt different types of assumptions and leadership styles. (Contains 5 tables.)