Background Our aims were to profile individuals unable to be recruited to a community based non-interventional study investigating warfarin safety, and to share the lessons learnt. Methods The target population comprised community-based adults stabilised on warfarin. Recruitment strategies included partnering with a third party pathology provider, an 'opt out' approach, and minimising the timeframe to recruitment. De-identified data for patients who could and could not be successfully recruited were analysed according to gender, age and reason for declining/inability to participate. Results Of 734 eligible patients, 486 were recruited successfully (66%). Of the 247 patients not able to be recruited, the median age was 79 years; 60% were female. Reasons for unsuccessful recruitment included: 115 (47%) 'opted out', 57 (23%) were too unwell, 39 (16%) due to health professional's recommendation, and 36 (14%) were not contactable. Successful strategies included the 'opt out' approach and using a known and trusted third party during patient recruitment. Discussion Lessons learnt are that multi-dimensional partnerships, including a familiar third party such as a pathology provider or doctor, could be of benefit. An 'opt out' approach, when not used as a substitute for consent, can also be beneficial for recruitment and decreasing administrative burden for GPs.