The paper presents estimates for the number of negative eigenvalues of a two-dimensional Schrödinger operator in terms of L log L type Orlicz norms of the potential and proves a conjecture by (see [11]). Upper estimates for N − (V ) in the case d = 2 can be found in [4,6,7,10,17,20,21,25,26,29,30,32] and in the references therein. Following the pioneering paper [29], we obtain upper estimates involving L log L type Orlicz norms of the potential (Theorems 3.1, 6.1 anf 7.1) and prove (Theorem 4.3) a conjecture by N.N.