Background: Preventive care is an important role for general practitioners, yet opportunities for prevention are often missed. Method: We provided an automatic electronic record preventive care reminder system for 12 preventive care activities for one 10 doctor practice. All patients who attended were randomised by the terminal digit of their record number. Results: The control uptake of opportunistic prevention was low; ranging from 1.5% (tetanus immunisation) to 27% (influenza immunisation). The reminders increased this by significant but small amounts for four out of 12 activities (immunisation for tetanus and pneumococcus and recording of allergies and weight), insignificant increases for four (mumps, measles and rubella immunisation, recording of smoking, and taking of cervical smears and of blood pressure), and insignificantly decreased influenza immunisation, and screening for diabetes and hyperlipidaemia. Discussion: Opportunistic electronic reminders have the potential to increase preventive care in general practice.