OBJECTIVE: In the paediatric intensive care unit (PICU), medication administration is challenging. Empirical studies demonstrate that interruptions occur frequently and that nurses are fundamental in the delivery of medication. However, little is known about nurse’s decision making when interrupted during medication administration. Therefore, the objective is to understand decision making when interrupted during medication administration within the PICU. RESEARCH DESIGN: A qualitative study incorporating non-participant observation and audio recorded semi-structured interviews. A convenience sample of ten PICU nurses were interviewed. Each interview schedule was informed by two hours of observation which involved a further 29 PICU nurses. Data was analysed using Framework Analysis. SETTING: A regional PICU located in a university teaching hospital in the United Kingdom. FINDINGS: Analysis resulted in four overarching themes: (1) Guiding the medication process, (2) Concentration, focus and awareness, (3) Influences on interruptions (4) Impact and recovery CONCLUSION: Medication administration within the PICU is an essential but complex activity. Interruptions can impact on focus and concentration which can contribute to patient harm. Decision making by PICU nurses is influenced by interruption awareness, fluctuating levels of concentration, and responding to critically ill patient and families’ needs.