Aims: To introduce the concepts “quality assurance”, “rational drug prescribing” and “outreach visits” in general practice in Storstrøm County, Denmark and study the effect of unsolicited mailed feedback and outreach visits on drug prescribing. Methods: The first step was to generate standardised charts displaying the county variations of drug volume prescribing within 13 major drug groups at the second ATC-level. The charts were mailed unsolicited to the 94 general practices in the county. Each practice could identify its position within the county prescribing variation. This procedure was repeated every six months from 1992 to 1998. In 1998 annual outreach visit were offered to general practice and 88 of 94 practices accepted. The awareness of prescribing profiles was monitored during the visits in 1998 and 1999. In 2000 a randomised controlled trial allocating practices into two parallel arms was launched. Effects of two desk guides on rational drug prescribing promoted during outreach visits were evaluated. Results: During the period of mailed feedback, there was a large variation in drug prescribing volumes between practices but little within-practice variation over time. No significant change was detected. Practitioners’ assessment of their own prescribing profiles improved significantly through the outreach visits. The prescribing of antibiotics was significantly affected by the desk guide whereas no effect was detected on the prescribing of non-steroid anti-inflammatory drugs. Conclusions: Semi-annually mailed feedback over a seven-year period had no significant effect on prescribing volumes or variations in prescribing volumes, but some effect on the practitioners’ awareness of their own prescribing profiles. Outreach visits significantly improved the awareness. A randomised controlled trial using outreach visits combined with a simple desk guide affected the prescribing of some antibacterial drugs as intended whereas the similar intervention had no detectable effect on the prescribing of non-steroid anti-inflammatory drugs.