Background: Strategies to implement evidence-based practice have highlighted the bidirectional relationship of organisational change on organisational culture. The present study examined changes in perceptions of organisational culture in two community mental health services implementing cognitive therapies into routine psychosis care over 3 years. During the time of the study there were a number of shared planned and unplanned changes that the mental health services had to accommodate. One service, Metro South, had the additional challenge of embarking on a major organisational restructure. Methods: A survey of organisational culture was administered to clinical staff of each service at yearly intervals over the 3 years. Results: At baseline assessment there was no significant difference between the two services in organisational culture. At the midpoint assessment, which was conducted at the time the Metro South restructure was operationalized, there were less positive ratings of organisational culture recorded in Metro South compared to the other service. Organisational culture returned to near-baseline levels at endpoint assessment. Conclusions: These findings are consistent with the literature that organisational culture is relatively robust and resilient. It is also consistent with the literature that, at any one time, a service or organisation may have a finite capacity to absorb change. Consequently this limitation needs to be taken into account in the timing and planning of major service reform where possible. The results also extend the literature, insofar as external factors with a high impact on the operation of an organisation may impact upon organisational culture albeit temporarily.