This paper discusses a longitudinal study that explored the relationship between use of organizational memory and knowledge (OM/K) and knowledge worker productivity within the engineering group at a nuclear power plant. Three data points were taken over five years. An Organizational Memory/ Knowledge Management System (OMS/KMS) was identified that improved the effectiveness/productivity of the organization. The basic components of the OMS/KMS remained the same over the study. A key and unexpected finding was that new members of the organization did not consider the OMS/KMS as effective as established members of the organization and tended not to use the system until they became established members themselves. To explain the success of the OMS/KMS, DeLone and McLean's IS Success Model was adapted to OM/KM. The paper presents this modified model.