Both hospitals and hospital patients are bearing a massive cost as a result of the occurrence of medication prescribing errors in the public health system (Bates, D., et al. J. Am. Med. Inform. Assoc. 8(4):299-308, 2001; Lombardi, T. Medscape Pharm. Online J. 02(1), 2001; Roberts, M., and Stokes, J. eMed. J. Aust. 168:317-318, 1998). Consequently, it is important to examine and address the possible causes of this problem. In this paper we suggest that poor information systems may be a contributing factor in the occurrence of these errors. We research this issue in an HIV ward of a large public hospital through interviews and a survey instrument. We find that in a significant number of instances prescribing errors are linked to situations where information is unavailable or inaccessible. This link, between problems in information delivery and prescribing errors, is a link whose extent has not been measured previously. It is, however, a link which exposes all stakeholders in the hospital system, the patient, the clinicians, the hospital, and governments funding prescription medications, to possible loss and damage and indicates a need for the implementation of more effective systems in this area. We use Reason's model for predicting systems error (Vincent, C. BMJ 316:1154-1157, 1998) as a tool to suggest that prescribing errors have an increased likelihood of occurring if one or more of the types of failure identified in the model are present in the existing prescribing information delivery process in the hospital. While Reason's model has been applied in a medical context, it has not been previously applied to errors which result from information systems failure. We feel that applying it in this way may shed some light on the causes of prescribing error.