The use of external labour such as temporary agency workers in the general workforce has increased in recent decades, but comparatively little is known about their impact within the aged care workforce. This article analyses quantitative data from a census of aged care facilities and a large-scale survey of their workforce regarding the use and impact of temporary agency workers on internal workers. It demonstrates that employing temporary agency workers helps address labour shortages generally and skill shortages in particular. However, it has a negative impact on the job satisfaction of internal personal care workers - a predictor of an increase in intention to leave. In contrast, there was little impact on internal nurse satisfaction. The use of temporary agency workers could therefore create a paradox: increasing personal care worker numbers in the short term, but negatively impacting on their retention in the long term. Given the need for an expanded and sustainable aged care workforce, this finding has important implications for organisations, policy and unions.