Aims: Investigate the number and type of tasks performed, delayed or not completed by regulated and unregulated (assistant) nurses. Background: Assistants in Nursing change the work environment of the nurses with whom they work. As the number of Assistants in Nursing working on acute units grows, it is important to understand how their presence influences nursing care. Design: Descriptive analysis of survey data from 62 acute nursing units across three Australian states between 2008-2010. Methods: All staff providing nursing care to patients were asked to complete a survey that included demographics, the number of tasks delayed/incomplete and the completion of six specific tasks. Nonparametric tests compared Assistants in Nursing (n = 25) to regulated nurses (n = 1630), and regulated nurses on units with no Assistants in Nursing (n = 1356) to those on units with up to 5% assistants (n = 76) and over 5% assistants (n = 198). Results: More regulated nurses on units with zero, or up to 5% Assistants in Nursing, completed tasks usually associated with assistants' scope of practice, relative to those on units with over 5% Assistants in Nursing. Statistically significant differences were found between the units in delays responding to the patient bell and in the planning of nursing care. Conclusion: This study suggests that Assistants in Nursing have an impact on the nature and timeliness of care provided in acute hospital units, that is relative to the proportion of staffing they comprise, to the effectiveness of integration and to the clarity of their scope of practice and associated delegation. Relevance to clinical practice: With increasing employment of Assistants in Nursing in acute hospital settings comes the requirement to optimise their use. This needs to include a well-articulated scope of practice, clear delegation of tasks and effective integration with the rest of the care team.