A study was undertaken to estimate the frequency of iatrogenic methadone toxicity in the first 2 weeks of maintenance treatment in NSW. Cases were identified from a list of all 1994 methadone-associated deaths using data on methadone patients held by the NSW and Queensland Health Departments. The likely causes of death were determined from data collected from coronial files. A forensic toxicologist experienced in the area gave an independent opinion. Of the 14 deaths in the first 2 weeks of maintenance, at least 10 were primarily caused by the toxic effects of methadone prescribed by NSW doctors. The rate of fatal iatrogenic methadone toxicity was 2.2 per thousand admissions to maintenance. Victims of fatal iatrogenic toxicity often displayed signs of methadone intoxication in the days before their death. They invariably died several hours after taking the fatal dose, usually after seeming to go to sleep. Often friends or family were concerned about their welfare, were unable to rouse them from their "sleep" and frequently reported the deceased was "snoring" loudly for some time before their demise. The author recommends that patients entering methadone maintenance should be informed of the risks and should be required to give written consent to treatment. To prevent fatal methadone toxicity, patients should receive daily medical assessment during the first 1-2 weeks of maintenance.