Our aim was to explore the attitudes and beliefs of healthcare professionals relating to the causes and reporting of medication errors in a UK intensive care unit. Medication errors were identified by the unit pharmacist and semi-structured qualitative interviews conducted with 13 members of staff involved with 12 errors. Interviews were analysed using a model of human error theory. Staff identified many contributing factors, including poor communication and frequent interruptions. Organisational factors included lack of clarity on the responsibility of the second nurse's check for medication administration, lack of feedback on medication errors, and a common and accepted practice of administering medication without a complete medication order. Barriers to reporting included administrative paperwork and lack of encouragement by management. Greater feedback on medication errors seems essential to improve current practice and increase reporting.