BACKGROUND Interruptions of hospital doctors' workflow are a frequent stressor, eventually jeopardising quality of clinical performance. To enhance the safety of hospital doctors' work, it is necessary to analyse frequency and circumstances of workflow interruptions. AIM To quantify workflow interruptions among hospital doctors, identify frequent sources and relate sources to doctors' concurrent activities. METHODS Within a typical hospital, 32 participant observations of doctors' full work shifts were carried out. Time-motion information was collected on types of workflow interruption and doctors' activities and analysed with logit-linear analyses. RESULTS The frequency of workflow interruptions was high, especially on the intensive care unit and emergency ward. Telephones and bleepers were the most frequently recorded type of work interruption. The combined analysis of doctors' activities and concurrent workflow interruptions revealed that the likelihood of the occurrence of certain types of interruption depended on the tasks being carried out by the doctor. CONCLUSION The present method may be useful for quantifying and distinguishing sources of hospital doctors' workflow interruptions and useful in raising awareness of organisational circumstances.