Ambulatory surgery has proliferated as a result of increasing inpatient costs. Its high level of safety has resulted in its extension to less healthy, often elderly patients. Patient compliance with instructions is essential to avoid morbidity. We aimed to identify subgroups potentially at risk due to non-compliance. A confidential questionnaire was administered to 220 consecutive daycase patients. Data included: patient demographics, duration of fasting, taking of medications that morning, importance of fasting and medication instructions, mode of post-discharge transport, and whether they had someone to stay with them that night. Seven (3.5 per cent) patients admitted to non-compliance with fasting instructions, with 8 per cent considering these instructions non-essential. Thirteen of 59 patients on medications took them against instructions, with 9 patients considering the instructions non-essential. Eight patients admitted intending to drive home; 7 per cent admitted to having no one to stay with them on the night of surgery. A significantly minority of patients (particularly male) admit to non-compliance with ambulatory surgery instructions; these figures may be underestimates. Absence of anaesthetic/medical input and lack of reinforcement probably contribute to non-compliance. Some medication-related non-compliance may be appropriate (e.g. antianginals, antihypertensives) and may reflect conflicting instructions given to the patient. The stopping of all medications prior to ambulatory surgery needs revision. Older patients living alone may not be suitable candidates for ambulatory anaesthesia.