The aim of this study was to gain deeper understanding of the work of nurses and shed light on the factors influencing their work in acute care. Professional nursing care makes a difference to patient outcomes. Therefore it is important to identify potential improvements in nurses' work to make better use of their knowledge and time for the benefit of patient safety. Method: Participants were 8 registered nurses (RNs) and 10 practical nurses (PNs) in one university hospital, observed during their work. Rich multilayer real-time quantitative data were collected with qualitative field notes on nurses' work, factors influencing their work, movements and time. Following each shift, participants were interviewed by observers. Data were entered onto a handheld computer and a digital recorder during observation. Data collection took place in 2008 and data analysis in 2009-2010. Results: Nursing work was characterized by frequent shifting of attention, interruptions, operational failures, multitasking and constant movements which influenced their work. On average, RNs and PNs encountered influencing factors 4.2 and 2.0 times per hour, respectively, the most common one being face-to-face communication initiated by a co-worker. However, participants described their shifts as quiet and manageable, and without interruptions and delays. Conclusions: Study findings provide a picture of the complex interplay of nurses' work, influencing factors and movements, with frequent attention shifting in chronological order. Participants were interrupted within an interruption leading to layers of interruptions, adding to the complexity of their work. Study findings demonstrate the importance of approaching and measuring nursing work as a complex phenomenon.