The decycling number, ∇(G), of a graph G is the least number of vertices of G whose deletion results in an induced subgraph without any cycles. Improved bounds are obtained for the decycling number ∇(Qn) of the hypercube Qn. Further, it is shown that ∇(Qn)=2n-1-A(n,4) if and only if Qn has a minimum decycling set that consists of pairwise non-adjacent vertices, where A(n,4) denotes the size of a maximum binary code of length n and minimum Hamming distance 4.