The British Society for Clinical Cytology Code of Practice on fine needle aspiration cytology complements that on exfoliative cytopathology, which was published in the last issue (Cytopathology 2009;20:211–23). Both have been prepared with wide consultation within and outside the BSCC and have been endorsed by the Royal College of Pathologists. A separate code of practice for gynaecological cytopathology is in preparation. Fine needle aspiration (FNA) cytology is an accepted first line investigation for mass lesions, which may be targeted by palpation or a variety of imaging methods. Although FNA cytology has been shown to be a cost-effective, reliable technique its accurate interpretation depends on obtaining adequately cellular samples prepared to a high standard. Its accuracy and cost-effectiveness can be seriously compromised by inadequate samples. Although cytopathologists, radiologists, nurses or clinicians may take FNAs, they must be adequately trained, experienced and subject to regular audit. The best results are obtained when a pathologist or an experienced and trained biomedical scientist (cytotechnologist) provides immediate on-site assessment of sample adequacy whether or not the FNA requires image-guidance. This COP provides evidence-based recommendations for setting up FNA services, managing the patients, taking the samples, preparing the slides, collecting material for ancillary tests, providing rapid on-site assessment, classifying the diagnosis and providing a final report. Costs, cost-effectiveness and rare complications are taken into account as well as the time and resources required for quality control, audit and correlation of cytology with histology and outcome. Laboratories are expected to have an effective quality management system conforming to the requirements of a recognised accreditation scheme such as Clinical Pathology Accreditation (UK) Ltd.