Organisations have invested in self-service information systems (IS) to provide a direct interface for service delivery. Enriching the usage of these systems can provide organisations with immense benefits. However, limited research has been directed towards understanding post-adoption IS usage behaviour in general and specifically in the context of self-service IS. This study proposes post-adoption IS usage behaviour as a broader concept constituting feature level usage of IS, integration of IS in the work system and exploration of new uses of IS. We evaluate how the new conceptualisation can be used to classify users at different stages of self-service IS usage. Further, we examine user perceptions that differentiate among the users situated at different selfservice IS usage stages. Data were collected in the context of a self-service Web-based IS to validate the post-adoption IS usage constructs and to examine the proposed thesis. The newly developed conceptual structure and measures for post-adoption IS usage behaviour exhibit strong psychometric properties. The analysis shows three distinct post-adoption IS usage stages and highlights that usefulness, user-initiated learning, ease of use, satisfaction and voluntariness of use differentiate users at the different stages of post-adoption IS usage. The results show that these variables aggregate into value confirmation and learning orientation as two higher-level concepts. Further, we evaluate the predictive efficacy of the research model in classifying users into different post-adoption self-service IS usage stages. Implications are drawn for future research.