A hierarchical cubic network was proposed as an alternative to the hypercube. By HCN(n), we denote the hierarchical cubic network that contains 2 n n-dimensional hypercubes. In this paper, using Gray codes, we construct fault-free Hamiltonian cycles in an HCN(n) with n ؊ 1 link faults. Since the HCN(n) is regular of degree n ؉ 1, the result is optimal. We also construct longest fault-free cycles of length 2 2n ؊ 1 in an HCN(n) with a one-node fault and fault-free cycles of length at least 2 2n ؊ 2f in an HCN(n) with f-node faults, where 2 2n is the number of nodes in the HCN(n), f ≤ n ؊ 1 if n ؍ 3 or 4 and f ≤ n if n ≥ 5. Our results can be applied to the hierarchical folded-hypercube network as well.