Also known as ‘expert systems’, these are computer software systems intended to help doctors make clinical decisions. Primary care medicine is especially noted for its uncertainty by virtue of being most patients’ first point of contact with health care, confronting the clinician with many ‘undifferentiated’ health problems. So far, these systems have not been as effective as expected because of a failure to analyse the needs of primary care. Simple procedures to prompt the delivery of treatment to patients with chronic conditions have improved care quality, but work needs to be done on their cost-effectiveness. The aim of more complex computerised support systems will be to forecast likely future events, and the possible effectiveness of proposed interventions, based on available information about the patient and an understanding of the risks and efficacy of interventions by doctors and other experts.