Let ℋ denote the Hilbert space of analytic functions on the unit disk which are square summable with respect to the usual area measure. In this paper we consider the formal differential exepressons of order two or greater having the form {fx321-1} and {fx321-2} which give rise to symmetric operators in ℋ. We show that these operators in ℋ admit self-adjoint extensions in ℋ.