Background: Healthcare workers (HCWs) will play a key role in any response to pandemic influenza, and the UK healthcare system's ability to cope during an influenza pandemic will depend, to a large extent, on the number of HCWs who are able and willing to work through the crisis. UK emergency planning will be improved if planners have a better understanding of the reasons UK HCWs may have for their absenteeism, and what might motivate them to work during an influenza pandemic. This paper reports the results of a qualitative study that explored UK HCWs' views (n = 64) about working during an influenza pandemic, in order to identify factors that might influence their willingness and ability to work and to identify potential sources of any perceived duty on HCWs to work. Methods: A qualitative study, using focus groups (n = 9) and interviews (n = 5). Results: HCWs across a range of roles and grades tended to feel motivated by a sense of obligation to work through an influenza pandemic. A number of significant barriers that may prevent them from doing so were also identified. Perceived barriers to the ability to work included being ill oneself, transport difficulties, and childcare responsibilities. Perceived barriers to the willingness to work included: prioritising the wellbeing of family members; a lack of trust in, and goodwill towards, the NHS; a lack of information about the risks and what is expected of them during the crisis; fear of litigation; and the feeling that employers do not take the needs of staff seriously. Barriers to ability and barriers to willingness, however, are difficult to separate out. Conclusion: Although our participants tended to feel a general obligation to work during an influenza pandemic, there are barriers to working, which, if generalisable, may significantly reduce the NHS workforce during a pandemic. The barriers identified are both barriers to willingness and to ability. This suggests that pandemic planning needs to take into account the possibility that staff may be absent for reasons beyond those currently anticipated in UK planning documents. In particular, staff who are physically able to attend work may nonetheless be unwilling to do so. Although there are some barriers that cannot be mitigated by employers (such as illness, transport infrastructure etc.), there are a number of remedial steps that can be taken to lesson the impact of others (providing accommodation, building reciprocity, provision of information and guidance etc). We suggest that barriers to working lie along an ability/willingness continuum, and that absenteeism may be reduced by taking steps to prevent barriers to willingness becoming perceived barriers to ability.