OBJECTIVE: The aim of the study was to assess the effect of the introduction of PACS (Picture Archiving and Communication System) upon image availability in an Intensive Care Unit (ICU) and the consequent impact upon the behaviour of the ICU physicians, in terms of the initiation of image-based clinical actions. DESIGN: A before and after study was used to compare the speed of image availability prior to, and following, the implementation of a hospital-wide PACS. SETTING: The research was part of an economic evaluation of PACS at Hammersmith Hospital, West London. PATIENTS AND PARTICIPANTS: All ICU patients who were X-rayed during two pre-PACS and one post-PACS data collection periods were included within the study. MEASUREMENTS: The times of: the X-ray request; acquisition; availability on ICU; and of any image-based clinical action taken by the ICU physician were recorded by radiographers and ICU physicians. RESULTS: PACS significantly reduced the time between request and image availability on ICU for routine X-rays but did not have any measurable impact upon the time clinical actions were initiated by ICU physicians. The data on non-routine images were statistically inconclusive. CONCLUSIONS: This study shows that PACS significantly improves the speed of delivery of routine images to the ICU, but it appears that the instigation of image-based clinical actions is determined by other organisational factors in ICU, such as ward rounds, rather than the availability of the image for viewing. Further work is required on non-routine X-rays to clarify the impact of PACS on physician behaviour in clinically urgent situations.