Access control has been an important security issue in information systems. Multilevel hierarchical information access widely exists in present-day government, military, and business applications. Extending access control design to work in a hierarchical environment is natural and necessary but rarely addressed so far in the literature. In this paper, a dynamic group-oriented cryptographic scheme to access a multilevel data hierarchy is proposed. In the proposed scheme, a trusted central authority is in charge of the administrative activities among the organization hierarchy. At the beginning, each user class submits its associated information and a cryptographic key of its preference to the central authority. Next the central authority generates a public information for each class according to their location in the organization hierarchy. The cryptographic key held by each class can be used directly as an encryption key to encipher data. These keys need not be modified when adding/deleting a class to/from the system. Compare with other existing schemes, ours has the advantages of flexibility in choosing user preferred cryptographic keys, cryptographic keys not exceeding a fixed length, reduced storage space in publishing pubic information, and protection from conspiracy attack.