Prescribing is one of the commonest tasks in daily general practice. Surprisingly there is little published research on errors that occur in this area. The aim of this study was to estimate the seriousness and level of prescribing errors that occurred in general practice. This prospective survey documented errors in prescriptions from 28 general practitioners as they occurred over a 3-day period in 12 community pharmacies. From a total of 3,948 prescriptions, 491 (12.4%) contained one or more errors. From a total of 8,686 drug items, 546 (6.2%) contained one or more errors. Of the errors the majority were minor (398, 72.9%), a smaller number (135, 24.7%) were major nuisance errors, and there were 13 (2.4%) potentially serious errors. The most common errors related to drug directions and dosage.