Long uninterrupted sedentary periods, independent of total sedentary time, are risk factors for poor health. There is little objective data relating to workplace sedentary behaviour and adherence to current recommendations. The sitting behaviour of office workers (n = 83) was quantified objectively using body-worn accelerometers (activPALTM) over a working week. Adherence to three different recommendations (maximum length of a sitting event of: 20 min; 30 min; 55 min) were assessed. Participants were seated at work for 5.3 ± 1.0 h/d (mean ± 1 SD), equivalent to 66 ± 12% of the working day, accrued in 27 ± 7events/d individual sitting events. Dependent on the recommendation applied, 5-20% of sitting events and 25-67% of time was accumulated in sitting events longer than current guidelines. No participants met the 20 or 30 min recommendations on every working day but seven (8%) participants met the 55 min recommendation. In conclusion, office workers spend a considerable period of their day sitting, accumulated in uninterrupted sitting events longer than current recommendations. Statement of Relevance: Emerging evidence suggests prolonged sitting has negative health effects. In this study of office workers, 25-67% of time sitting was accumulated in events longer than minimum recommended durations. Adverse sitting behaviour is prevalent in the office, making it an appropriate setting to target the reduction of this behaviour.